Major Description
They appear to be swapped, though that is not quite the case. You can consistently see COMBINE_INPUT_RECORDS < COMBINE_OUTPUT_RECORDS, which shouldn't be possible.
This issue relates to TEZ-1344, which was closed due to not being reproducible, but it actually is fairly easily reproducible if you run the same job on Tez and on MR. For whatever reason, I cannot reopen that Jira, so I'm creating this one.