ToolTips not being displayed when using an existing ActiveX control in a .Net Form

[ADavis]

We have an existing ActiveX control that plots data points over an
image. When the mouse is moved over these points, a tool tip is
supposed to be displayed indicating information about the point.

This control is already deployed in an unmanaged application and works
correctly there. We have been attempting to re-use it in a .Net forms
based application and have gotten all other aspects to work except the
tooltips.

The ToolTips simply do not display when the control is hosted in the
ActiveX form.

Using Spy++ we can observe the message exchange betweeen the control
window and the tool tip control window. As near as we can tell, they
are identical. In the .Net app, we definitely get the WM_NOTIFY
messages for text request and pop.

I haven't found anyone reporting a similar issue, so I'm not sure if I
am doing something wrong or just something bizzarre.

Thanks for any insight,
A