There are many variations of this bug and I'm sorry if it's been brought up before. I did a search and found nothing. Basically I can't have: .txt files open in Mousepad .pro files open in Qt Creator Since they are both the "plain text document" type, I have to choose one or the other. Obviously I don't want my .txt files to be opened in Qt Creator, nor do I want my .pro files to open in Mousepad. My workaround is to have all "plain text document" types open in Mousepad, and then I right-click on .pro files and select Qt Creator (below Mousepad). This isn't too annoying, but should probably be fixed. Thank you for your contributions. Xfce is sweet and stable. Every other desktop I tried had bugs much larger than this. I am using Debian Stable (Squeeze) Xfce.
The proper way to handle this is by creating a new MIME type for files with the .pro file extension: https://developer.gnome.org/integration-guide/stable/mime.html.en