I have absolutely no clue why is this happening, I have never seen anything like this before.
If you want I can try to go through the plugin line-by-line to see if at any point of execution triggers anything. For that however I need back-end access to clear the cache, and (s)FTP access to make direct modifications to the plugin quickly.
I can only assume, that something somewhere triggers something else in a different code, but no error messages, nothing whatsoever.
However first try turning off all the other plugins to see if anything changes. If not, then switching the theme. That narrows down the issue to either a specific plugin or the theme, and it might be easier for me to cross check.