The drop-down menu in the form triggers the onclick function twice, once on clicking the drop-down and second on selecting a menu option. This is a change from the old 12.9 release of Service Catalog.
Release : 17.2
Component : CA SERVICE CATALOG
The behaviour of select field on-click has been standardized to be inline with standard HTML select field behaviour. Onclick will be triggered on every click, not merely the selection of the drop-down item.