Steps to reproduce:
1. Create new project in Unity
2. Close and Restart Unity to project selection window
3. Delete folder project from disk (while Unity is in project selection state)
4. Switch back to Unity and open the project
5. Unity doesn't remove project from the list.

Expected result:
After clicking on project which was deleted from disk while Unity is in project selection state, Unity should refresh project list and remove project from project selection list.

Workaround:
Quit Unity and open it again.

Reproduced with: OS X 5.4.0b12
Not reproducible with Windows