FYI, I happened across this commit comment:
3f902354b08ac788600f0ae54fcbfc1d4e3ea765
| So, let's accept the removal of the guarantee about
| the output tuple's rowtype marking, recognizing that this is a API change
| that could conceivably break third-party callers of tupconvert.c. (So,
| let's remember to mention it in the v10 release notes.)
..but couldn't see that the commit or change is so referenced.
Justin