In fact the way the combobox is displayed in the Visual Builder is in it fully extended state.
So it's in the Visual Builder that you define the maxium size for the combobox, this is a great behaviour.
Perfect if you add the default height of 100, but the reason why i make mistake here is that the small triangle at ritgh is vertically centered on the combobox in the visual builder so it's like if it's a very big one for big characters

Thanks a lot, I completed the ComboBox_lib.ppl

I have not yet tested including the file as a include lib in ppl, but it work by copy paste in my apps.
Regards,