It looks like our plugin (Copyright Proof) doesn't work with yours. After investigating a weird problem for some time, our user told us this: "I managed to find out what other plugin is causing your pluging not to work properly. After having deactivated all and re-activated. It is: "W3 Total Cache". I think there is some documentation available on making your plugin work with W3 Total Cache."
Is there such documentation? I couldn't find it.