Turns out the difference is not between 7.6 full and compiled versions, but between 7.6 and earlier versions.
In 7.1 (which is what the client was running before being upgraded to 7.6 compiled) RBTI_FORM_MODE was evaluated and available in the BEFORE START EEP. In 7.6 however, RBTI_FORM_MODE is NOT evaluated until the AFTER START EEP. If a form was already used in the R:Base session and the RBTI variables were not cleared, the form mode of the _previous_ form is stored in RBTI_FORM_MODE. If no form was used, the variable does not exist. Kudos to Mike for pointing me in the right direction. I'm now off to find all instances where I used RBTI_FORM_MODE in the BEFORE START eep. -- Larry
