You can have a dynamic dropdown list with dynamic screen tip text if you want.
In the example there are various combinations of static and dynamic values.
The first dropdown has dynamic tip text but in order to get it it clears out the static xml drop down list values. If you remove the getItemCount callback then the list is static but so is the tip text.
So it appears the mixing of static and dynamic does not function as required. But all static or all dynamic should.
