I've noticed a different bug. Sometimes if I delete a module from a rack, or 'cut' it out using CTRL+X, the module itself will disappear, however that module's gray information window--the one that usually pops up when you mouseover a module--will remain on screen, moved to the upper left corner, and never goes away. Refreshing the page fixes the problem. I've tried to replicate the bug deliberately and I haven't been able to do so consistently, but it does happen sometimes.