ComboBox Problem

I'm using the combobox.cs example from http://www.unifycommunity.com/wiki/index.php?title=PopupList for a few GUI elements that need this, however thehre's a problem with it:

The selection is called each time OnGUI is called, However I need this call to be made only once when the selection is clicked.

Also, how do I get breakpoints to work in monodevelop? This is probably the main reason I can't figure out what's going on...

I would be grateful if you could enlighten me on both questions