The BallonTip timeout is only respected if the shell detects the “user presence” (i.e. mouse moves or keyboard input). If none of these happen (because you are watching the bubble) it will sit there [indefinitely]. The logic behind this design being that users should not miss notifications when they are away from their machines. This is the “By Design” shell behavior.

[http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/ 52e33b59-e27f-4eec-a8c7-34278279239a]