Comment 28 for bug 402892

Just got this when dragging a file from file-roller to a nautilus window on Ubuntu 16.04 64-bit. Nautilus would scroll its window up and down in response to the vertical position of the mouse pointer, but no button events appeared to take effect in any application. Had to Alt-F2 and pkill file-roller to get control back.

It's unlikely to be a fault in a specific application, more likely a flaw in the desktop inter-process signalling system, for which there are several bugs open. It's difficult to pin down though as it seems hard to produce a useful test case for this intermittent problem - I'm a regular Ubuntu user and this occurs very rarely (in my experience so far).