Can't click files/folders in Thunar

I'm using a new install of Mythbuntu 10.04. I can usually click on one folder in Thunar. After that, attempting to click or select any folder or file does not work. If I click and drag, it creates a selection box, but nothing gets selected. If I use the arrow keys on the keyboard, the file/folder will appear to select, but pressing "Enter" does nothing. If I try to back down to a lower level, I still can't click on any other file or folder.

I installed usbmount (and pmount as a dependency) to auto-mount my USB drives that I have connected. I don't know if the problem existed before, but I noticed this after I installed them.