well, what you could do is reset it.
1. go to "my-documents", find the HPL folder, and rename it to "HPL_OLD"
2. restart the level editor (after doing this, there should now be a new HPL folder in your my documents folder)
3. delete the HPL_OLD folder (this completely resets anything in the level editors' settings. its sort of as if you downloaded it onto a brand new computer. (maps wont be changed though, only the "recent files" list will be deleted, along with some other things. dont worry, it does NOT harm any work youve done)
let me know if the problem prevails
and also, if you have any other problems in the future, post them here:
http://www.frictionalgames.com/forum/forum-39.html