Sounds like this bug:
Bug 21116 - Calendar headers won't disappear after viewing a shared calendar event Bug 21473 - can't open exchange appointments (dupe)
This was fixed in 5.0 GA - if you're running 5.0 and still see the same bug, can you please provide some more info:
- What browser?
- If Firefox, append "?dev=1" to the url and try to repro.
- If you're able to repro, open the javascript console (via Tools menu of the browser window) and post any
JS *errors* (not warnings)
Thanks.