You can restrict the entries to the contents of the value list in the fields definition by clicking on the Validation tab and the checking member of value list.
But, as you've noticed this is a limitation of Go at this point in its development cycle. I could get the typing to work correctly in the same type of field. Might be the trigger I was using when it was using it as a popup men.
Maybe we could convince the engineers to give up the monster wheel in favor of a mimic of Pro?
Still, at just $9 Go is the bargain of the century. We just have to rethink our designs and keep our fingers crossed.