Reinvestment rate?

Not sure if you are describing the below as I thought I had the same problem.
Its very misleading and after a lengthy call to RS and some fiery conversations with the support team I came to this conclusion.

Historically rolling loans used to get fully repaid @ 1month (All the funds were yours to do what you like with)
Now however the rolling loans use the same % for the life of the loan, and the monthly repayment+interest will be put to holding/market at the rate of your choice.
RS are still using the old format/coding for rolling loans, lets say you lend £1000 at 3.9 for 30 months. Each month when you are due a payment on this loan, RS will pretend the loan is fully repaid and then send a new order to market at the original %, this action will send you an E mail to say a new loan of XXX has been formed at 3.9%. But this isn't actually true in the real world. (the loan doesn't fully get repaid and then re lent to the same borrower)
You can check this on your transactions, it shows as if the loan has been fully repaid and then the remaining amount has been re lent. The re lend causes the Email to be sent. When in fact this is not true and very misleading.  The new loan is given a completely new loan ID as well.
If you look at your future cashflows this is also very misleading as it shows you that the loan will be fully repaid + interest, and you don't know what the monthly outstanding amount will be. When you drill into the repayment schedule you will notice rolling loans only have 1 payment.

Rolling should be re programmed as per the 5yr loans, and you should only see the monthly repayment+interest in both the transactions and future cashflows
I hope this makes sense and could be the cause of the confusion. 

I have spoken to them on 3 occasions about this issue (and other issues) and I basically told them they were lying and their supervisor/Trainer is incorrectly telling you whats happening and you are misleading the public.
After about 30mins on the phone, I managed to get one of the customer service people to understand that the loans aren't fully repaid each month and a new amount re lent. (in the real world) I asked him: what's the difference between the rolling and the 5 year, he then he reverted back too the usual line 'now we use the same rate for the life of the loan' I said so how does the 5year work ?  I think then the penny dropped :-) 
They all also tried to tell me that the capital and interest that has been repaid on rolling loans has to be reinvested every month otherwise if I withdrew it I would be penalised for 14 days? - Again a lie. (This explains why holding is not an option in the reinvestment function for rolling)
 I said this money isn't matched so surely im free to do what I like with it, you can't penalise me for unmatched money - Again he confirmed I would be, and the reason is to stop people manipulating the market ? I said so in rolling I have to reinvest and 5 yr I don't - YES (this is not true)
RS need to retrain their staff as the information they are telling us is very misleading, I believe one of the reasons is because of the way their system is coded, sending E mails with a new loan ID's and doesn't show you a repayment schedule on rolling loans. 
IMO the Rolling works exactly like the 5 year, the main differences are.
Rolling you have NO idea on the term of the loan pre matching and you are able to withdraw the money with no penalty. (market conditions apply etc etc)

Yes, its very very misleading the way that RS explain it . The confusion starts when RS tells you the money is repaid and re lent at the same rate in the rolling giving you the impression thats means forever or until you remove the money, (14 days lock out) but when they say you are contracted to the same borrower for the length of the loan. This makes you think the amount isn't fully repaid and then re lent. (which is how all their computers are programmed).IMO rolling works just the same as the 5yr - I believe  - It would be nice if RS can confirm and just explain it to us like this.

I did exactly what you are suggesting as my money was matched at 2.4-2.7% I cancelled it all , invested a lot in 1yr and 5 yr and now getting between 4.2-4.8% in rolling. Your analogy above is correct. If you sell out of everything wait the 14 days, when you reinvest will get the rate the day you invest for the length of the loan, (just like you would in the 5yr) they are standard amortising loans, but you will not know the length of those loans until you look at your loan book after they have been matched. We are told they won't be 5 years, however I have some money match upto 48months!
Every month you will receive a repayment (you won't know what this is though unless you have all your loans set up on an excel spreadsheet) and depending on your instructions that cash can only be reinvested at either market rate or one of your own but you can't send it to holding.
So another issue you will find - depending on how much you invest : Once your money is matched and you find out the repayment dates, note the minimum re-investment is £10. As rolling doesn't let you send the money to holding, these funds can't be added to funds being repaid from other markets which are sent to holding.You could get a situation where you have such small amounts repaid every other day and it takes you almost 2 weeks to accrue £10 to reinvest.
Personally I like to get all my money paid to rolling at a very high rate, I then cancel those orders so the Money all goes to holding and then manually place 1 order to the market to avoid me having lots of small loans in the future. (I hope that makes sense)
Something so simple now seems so confusing..
Good luck

And it's just plain annoying not being able to consolidate tiny amounts of money into one decent sized loan.

Are you sure this has happened ?
check your transactions tab, see if all of your money was re lent , or was there a small amount left over ? This should be the interest and the monthly capital repayment
Money technically isn't re lent, as its not being fully repaid, its always on loan to the same borrow - just like the 5YR. In this market you get a monthly capital repayment + interest.
Yet in the rolling RS tell you they repay all of the money and then set a new loan up at the original rate minus the monthly repayment + interest and then send you an E mail to say you have a new loan., giving you the impression you have re lent the money.  
Read all of the conversation above to help explain the possible confusion OR maybe you have a different issue and you will need to call RS