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What is the trigger for this EpiBinding, DB Field, or Like?

My assumption is that it would be on the DB Field, but it does not seem to trigger when I have on Supplier Maintenance : Supplier ID and Supplier Price List : Supplier ID. Same Like, same DB Field, but different EpiBindings. Assumption again after investigation is that this behavior is based on the EpiBindings, and this is by design / as intended and not a bug.

Would anyone please clarify for me. Thanks!

Anyone know the answer here?