ComboBox closes immediately on .NET 2.x

[Iluvatar]

Hi everybody,

a few weeks ago we moved some old windows forms based application
to .NET 2.x. We had no problems so far, but some ComboBoxes now have a
strange behaviour. When the form opens the first (!!) time and one
clicks the dropdown, the list opens but closes immediately again. If
one is holding down the left mouse button, one can select items from
the dropdown "as normal".

Now if you close the form and open it again, the ComboBoxes have the
expected behaviour, which means the dropdown stays open, after
clicking on it.

Any ideas how to investigate the problem? No exceptions or else are
thrown.

Regards,
Michael

 

[Guest]

do you have any kind of handler attached to dropdown control? or any hooking
to its messages in WndProc?

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[Iluvatar]

Hi,

thanks for your reply.

do you have any kind of handler attached to dropdown control? or any hooking
to its messages in WndProc?

No, there's no handler or hooking in WndProc. I tried to test if the
control looses focus, but this does not happen.

Regards,
Michael