Probelm on minimzing a non Delphi window

I have a problem when minimizing a non Delphi window which was created by a
Delphi application.  When the window, in this case HTML Help, is minimized the
MDI Parent form appears to get the keyboard events even though there is a
valid MDI child from open.  The mouse events appear to be handled by the
correct form, ie if over the MDI child the child gets the mouse events.  In
addition if you click on the child form the child does not appear to get
input focus.  If the HTML Help form is closed rather than minimised the
application works as expected.

Any ideas?  The application appears to be getting the correct windows
messages.

Thanks in advance

Brett