well, thats the only time it can happen, by my way of thinking. since the very beginning of potential, the pillar of my understanding of potential with respect to player growth was that the rate of improvement (positive or negative) was tied to the amount of growth left (this has since been confirmed by admin, but still). this led to my 0 minute practice theory (0 minutes in a capped category wont hurt you) that i had to defend for a good year or two before people decided to try it instead of simply proclaiming me wrong by pasting that CS ticket where admin said 7 minutes (not that im still bitter or anything, lol).
anyway, by that theory, the only way you can decrease from a capped or very close to capped position is through offseason improvement (i wish deprovement was a word, it would fit so much nicer with improvement than decrease or defining improvement to include negatives!). so i am pretty sure thats the only time you could see it. admin has already admitted the bug, and said he can't fix it (well, won't because its too hard to be practical, in case the word mincers come along), so i think we can safely assume that is the problem and that we just have to live with it.