GTK1.X, GtkCombo updating on OSX?

What is the method that's called when you click the down arrow button on a 
gtkcombo widget? I'd like to directly control this if possible. 

Reason: The GTKCombo widget isn't fully updating for me on OSX (works fine on 
windows) until after the down-arrow button is clicked three times: 

1) drops down the combo, but the scrollbars aren't resized. 
2) raises the combo 
3) drops down the combo with the scrollbars resized. 

Screenshots available here: 
http://chico.benjamindsmith.com/phpgtk_osx/dropdown/

Thanks, 

-Ben

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