There are 3 keys that might cause exiting the field to occur. Which, if any depend on behavior options specified for the field. They are:
Tab (Char code 9)
Return (Char code 13)
Enter ( Char Code 10)
See where the 9 comes from?
You need to rewrite the If step to read like this:
If [ Get ( TriggerKeystroke ) = Char ( 9 ) ]
Thank you for the excellent response. It was hugely helpful!