When I use Lord Scourge as a tank, mount and dismount, he loses all buffs. So far it only happens with Scourge and only as a tank. Interestingly, if I set him as a tank, buff him, mount and dismount the buffs are gone, but if I switch him to heal afterwards the buffs reappear (without applying the buffs myself of course).

Nothing breaking but very annoying.

Lokin has the same problem, and it's gone untouched for years. After seeing your post, I went to check and he has the exact same issue as Scourge that you describe. If on tank or DPS, no buffs will stay, but role set as healer works as it should. It's got nothing to do specifically with mounts, just when he is summoned in those two specific roles.

I wonder if Scourge's increased damage intake is as bad as Lokin's as well, something else to test out.