I've found the reason, I think. The window is redrawn by necessity whenever the window is resized, and hitting alt in Firefox with a hidden menu bar causes it to act as though the menu bar has appeared (it actually does appear if you only tap alt). This resizes the page due to the way firefox handles hidden toolbars and forces the redraw. I imagine the same might occur in Chrome with autohidden toolbars in Chrome's fullscreen, but haven't tested this. I've worked around it in my browser by installing an addon which adjusts the way the various toolbars are displayed and running in fullscreen mode (which actually ended up making roll20 even nicer to use =D ). The addon in question is this one ( <a href="https://addons.mozilla.org/en-US/firefox/addon/fu" rel="nofollow">https://addons.mozilla.org/en-US/firefox/addon/fu</a>... ) for those who run into the same issue and similarly refuse to set the menu bar to always show. So really, the bug still remains, but it's different to what I originally described. After some additional testing I believe the ACTUAL bug to be this: If the window is RESIZED while dragging and dropping an element from the Art Gallery, causing the Art Gallery (ie. the source of the dragged image) to refresh, then the item's preview is not correctly removed. Of course this situation is reasonably rare, but it should still be patched out. Additionally, this implies that there are other, more common use cases which will trigger this bug . Consider the case where I search for an image (leaving the search box focussed). I then start dragging an object. I hit the 'w' key (Advanced shortcuts) to hide the sidebar. This seems like a perfectly reasonable thing to do, as I want to see the map to place the item. At this point, the behaviour splits based on if the search box was still focussed. If the search bar is NOT focussed (say, because I clicked one of the favourite stars) then this works as one might expect. The sidebar slides out of the way, and I can see the full map to place my item. However, if the search bar IS still focussed I'll accidentally append a 'w' to whatever I had searched for, causing the search to trigger again, the source of my dragged item to disappear, and the preview to be stuck forever wherever my cursor happened to be at the time. That might have been hard to follow, if you need more info on the bug please say so. I guess the most generic way to describe this would be: If, while dragging an item from the Art Gallery , the Art Gallery is refreshed causing the source item to disappear, then the preview of the item which was being dragged is never removed. You should be able to replicate this in Chrome, or anywhere :) (Edit: Typo fix)
