Problem with toolbar in ActiveX control - sometimes displays behind parent window

I'm using tooltips in one of my ActiveX controls. I do it per KB article #141871.

Works fine, except:
- The first time a web page is opened with this control, the tooltip works fine
- If you open another app and return to the web page, the tooltip still shows up but BEHIND the parent (IE browser, in this case) window. (I know this because some of the text strings are long and I can see them 'behind' the IE window)

The control acts the same way if used in a CHtmlView-derived child window in an MDI app.

Any ideas how to fix this?