Hello yc,
There seemed to be something going on here, and I have filed a report with our R&D department to look into it. As a workarond, you should duplicate the control before associating a tooltip to the control. If you duplicate the control n times, then associate tooltips with your duplicate controls and with your original control, and you should see the correct behavior.
Hope that helps.
Wendy L
LabWindows/CVI Developer Newsletter