PropertyGrid in a taskpane - drop downs not working

I've successfully created an add-in which operates out of a Taskpane, however I'm having issues with the PropertyGrid control.

I can add and change property values fine, however none of the drop down boxes work - the drop down arrow is shown but it just flashes if I click on it (for Booleans, string arrays etc). I've tried running the same code in a separate windows form and it functions fine - it's something to do with being imbedded in the taskpane.

Does anyone have any pointers? Does the property grid work ok for anyone else?

Cheers

SolidworksApi macros