Possible errors in "available" figure

Not a big problem, but I've just had a written dialogue with FS and they admit that the "Available" figure could be incorrect (due to series of combining errors) for a period of up to a few hours at any one time.  I'm not sure if this error is well known so I thought I'd add a thread.  I've only run into this fault once or twice (not sure about the twice) over the past 2 1/2 years so I suspect the probability is relatively low but it is best that we know.

I'm advised that fault has been elevated to IT.