NIN's poison wearing off after level sync

It's been bugging me since I noticed this and frankly, I don't understand the reason.
When syncing on lower level FATEs, dungeons or trials, I get that our buffs/stances get removed (although there would be a work-around but that's another topic). But when leaving these events, the ninja's Kiss of the Wasp and Kiss of the Viper get removed. AST's sects stay, buffs like Protect stay, tank stances also stay, only NIN (I haven't tried other melees on this) gets their stance removed. Heck, even CLeric Stance stays.
Why? Is it a bug? Is it intentional? If so, what's the reasoning behind? It is very annoying that's for sure...

Very odd.
I would guess it's because the strength of the Ninja poisons is altered by traits. So maybe the game can't sync the effect of one that's currently applied up to the traited version and instead removes it to force you to recast.

This happens with any stance or action buff. This is why I like using dragoon for beast tribes because it's the only melee that doesn't have to reapply their damage buff action when they level sync. Nin has poison, MNK has fire stance, tanks have dps stances, smn loses aetherflow, healers lose cleric stance, etc. This has been a complaint of mine for a long time because it makes _no_ sense that when you sync to a lvl you have an ability you lose that ability and have to reapply it.