It shouldn't be flagged on the latest commits (since March 28th, so this is included in the latest & prior release binaries).
Each contest participation grants 20 OT affection regardless of who is the current handler. This 'fact' was unknown to the community; before this, PKHeX had cleared the OT Affection when 'fixing' memory data. Now with it known, PKHeX doesn't clear the affection on synth-trade, and permits n*20 | 255 OT affection on past gen pkm.