"Some applications can change the default application to open directories from nautilus to another application. For example, I did it once with Krusader by following these steps:
1) Right-click any folder in Krusader
2) Choose "Open with -> Other..."
3) Choose any application (e.g. I chosed smplayer because I wanted it to play this directory as a DVD Video)
4) Mark "Remember association for this type of file

From now on, clicking Places -> any folder causes Smplayer to open the directory. There is no easy way to fix this as directory properties window in Nautilus doesn't have a tab to set a default application (it only has one for files). The only way to fix this is editing .local/share/applications/mimeapps.list file manually which is not especially user-friendly."

This bug was originally reported by Michał Gołębiowski on Launchpad in Ubuntu at <https://launchpad.net/bugs/482949>.