When you perform an action which requires Outlook to launch an explorer window, I've noticed some strange behavior.
1) When I first installed Office, created a new email, and attempted to embed an image file into my email body, the explorer window was non-functional. The drop-down directory list was cycling through different directories as if a key was depressed. When I tried to fix it by using the quick list of shotcuts on the left hand side bar, even they would not respond. Finally, I click on Recent and that caused it to return to a normal state so I could browse my hard disk for a file.
2) After I got it a little better under control, I noticed that sometimes the drop-down directory simply won't respond.
Still need to test this further to see what might be causing this and if there are straight forward fixes.