I've shared a few A/P stories over the last few days, so it's only far to turn to our A/R crowd for another new bug we found in R12! A few months after we had R12 up and running, all of a sudden a certain type of receipt was not allowing us to create credit memos on the invoice and all we were getting back was the error code "AR_RW_GL_DATE_BEFORE_CM_GL". At first I thought it was a custom type of error message because it was very rough, and not what I was expecting from Oracle API error codes, so in searching My Oracle Support I was amazed to not only find it but I also found note 1393304.1 detailing how this was one of several error codes ("AR_APPLY_BEFORE_CM" is another) did not have their robust error reporting defined.
This bug is the exclusion of several error descriptions from FND_MSG_PUB.GET, but it could have been found and reported on before we had R12 in place if we had test cases for a bad data scenario like this. As with several other R12 posts recently, this isn't to highlight Oracle in a negative light, but shine a positive light on the ability to find these items prior to your deployments with stronger test cases and more rigorous testing.