Configuration is lost after reconnecting the Matrox

I'm assuming that you're using this with a Mac. I have limited experience with these Matrox devices but I've installed and troubleshoot a couple of them.

What you're describing sounds like a possibly corrupted preference file or support file, that the Matrox Powerdesk software relies on to determine the settings you have defined. I would troubleshoot it by removing or renaming the following file, which should force the Matrox software to create fresh copies of the files.

User/~/Library/Preferences/com.matrox.powerdesk.plist

Good luck!