Just tried it on one window. It works for me.
Don't know if this is a Finder issue or a System User Interface issue, or something else. To find out if it's one of the above, use a trial and error method: one plist file at a time. Not very sophisticated, but Mr. Sophisticated hasn't posted.
/Users/YourUserName/Library/Preferences/com.apple.finder.plist
/Users/YourUserName/Library/Preferences/com.apple.systemuiserver.plist
Move one to the Desktop.
Restart.
No good?
Try the other one.
What happened?