False alarm, this was self-inflicted.
The original ROM for my car doesn't have this problem. I just found the revision of my ROM where this table changed, and my notes indicate that I was tinkering with WGDC around that time. My guess is that I intended to extend that compensation further down to the left and somehow managed to screw it up royally.
Yikes. Time to pull out Freon's SimpleTune and go through all my changes table-by-table.