Windows form in an in process COM object

[PLS]

I'm writing a extension to an existing app that supports COM objects for
extensions. The extension is written as a .NET class library with the
exposed class creating a Windows form and call ShowModal. The form
appears on the screen, but does not respond to mouse and keyboard input.
It is as though the form is not receiving Windows messages.

The hosting app provides a standard Windows message loop, which is
basically
GetMessage
TranslateMessage
DispatchMessage

Is something more needed? ShowModal should provide its own message loop,
but does the .NET runtime depend on having an Application object
somewhere down the stack?

++PLS

 

[PLS]

Just for reference, if I display the form with Show rather than
ShowDialog, everything works. Only ShowDialog fails.

++PLS