I finally found that file Copy/Paste bug that I often encountered but found hard to bug reproduce.
Right, I am guessing it seems that XnViewMP is using it's own background 'Clipboard' and not the same Clipboard as that of my system (Windows).
1.) Open a picture to view in XnViewMP (I open from "recent files")
2.) Wait a few seconds
3.) Now press "Copy" command in XnViewMP for the same File (Edit>Copy OR use "CTRL+C")
4.) Now close the XnViewMP application (press "x" on windows title-bar)
5.) Now try to Paste the file anywhere in Win Explorer....You can't
....However if you keep the program open (step #4) and attempt to Paste, then pasting the file works as normal.
