Custom GUI's bug with object output,

Hi, I was working on my mod and I found a bug. I asked on the issue tracker about how to fix it and I didn't really get what to do. The bug is that when seting a procedure for "When slot content changes" on a crafting table like GUI, the procedure is done only when the item from one of the slots is removed and not added. Klemen gave an explanation wbout what I should do in this case, but as I said I didn't get it. Please help me, it's very important.