Forms 10.3.1 appears to be secretly stripping quote (") characters from the values set in the form before passing the data to lookup rules. We verified this by writing a stored procedure that simply returned "hello world" as output and stored the value passed from forms into a table. The value was sure enough missing the " character.
The modification of data causes the lookup rules to return nothing, since the modified value will never exist.
Any way to disable this?