OCM_COMMAND message issue

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MFC

VC++

i have a mfc olecontrol being used in an c# form. For this drop down control i have a mapped OCM_COMMAND message.

When i open C# form for first time, and if i click this control OCM_COMMAND message will be fired whenever i click on drop down control, but if i hide and open the form again this OCM_COMMAND message will not be fired even if i click on drop down control

I have observed hwnd of this control will be unique int for first time. But after re-opening the form hwnd will be zero

What I have tried:

I tried using SW_ZNOORDER flag while creating the control. But it didn't work.