I was working on a validation rule formula, and noticed that whatever criteria I provided, the formula was returning true. I stripped out the criteria in the formula, until I had a simple formula:
ISBLANK( BillingState )
This formula is returning true regardless of what I put into the standard
BillingState field on the standard Account object.
Once I add a value to the field, I would expect
ISBLANK(...) to return false, and allow the record to be saved, but this doesn't seem to be the case.