On Win7 x64, it sometimes happens that dragging a file from Windows Explorer into PSPad makes the PSPad window lose focus, and it's entirely possible that another fullscreen window receives the focus. I haven't found a pattern for this behaviour yet, so I'll try to reproduce it a few more times and see if I can notice anything.
-- <http://forum.pspad.com/read.php?2,61780,61780> PSPad freeware editor http://www.pspad.com
