Workaround - don't press ESC when holding the mouse button down. Instead, continue to drag mouse to an area that won't accept it (normally cursor is a 'No Entry' type symbol). Release mouse there and then go and re-select the entry you wanted.
This workaround does not apply for the actual use of the drag function into a web form (example) where the UI shows the same symptoms. The ESC method was simply meant to be a simpler way to reproduce the problem for troubleshooting purposes.
The problem appears on a "regular drag and drop" as well, if you return to PasswordSafe immediately after the operation. This is annoyance when trying to open multiple tabs for, say, checking a few webmail/social services at the same time.
Should be fixed in the next release (after r5254). As temporary workaround you can press F5 (View->Refresh) to restore focus bar.