This one has been annoying me recently and I imagine it was on the old tracker. Basically, if you use banishment or direct banishment and then cast root on the mob before the temporary root effect fades it will break the new root as well. The really odd part is that the new root spell you cast will still show up on the mob even though it's not actually rooted. This makes it really difficult to punt and park something out of the way and obviously it's a bug to see the root debuff on a mob that can walk around unhindered. I can't say I've tested it everywhere or on lots of different mob types but it sure happens on giants in Kael very consistently.
Looks like this applies to all roots. If you can stack 2 root spells on a target, the first root break will free the NPC even if there is a second root. Not sure how fixable it is but can look at some point. The knockback distance is affected by how many players are in the zone. Not sure why, but I think that one is much more challenging to fix.
Sounds the the root flag is different than the spell itself and when a root spell lands it adds a root tag and when the root spell wears off it is removing the root tag meaning even if another root spell is on it the tag is still removed freeing the mob.
I realize it won't fix the bigger problem but Ranger's Flusterbolt is very similar and it puts root in slot 2 which is what all the normal root spells use. And it looks like the normal root spells always overwrite each other even if they're lower level. So, I'm guessing if it were changed to slot 2 I could overwrite it with a regular root and the problem I'm seeing would be more or less fixed. Vinelash and other similar abilities look like they're using slot 2 as well. Although, I've got no idea if it was put in slot 12 for a reason. Maybe enchanters aren't supposed to be good at punting and parking mobs with root like other classes. However, it's already pretty limited since the enchanter version is only 3 ticks of root while other classes are 6 or 7.
This issue has been fixed internally and should go live with the next monthly update. NPCs with multiple root spells on them should remain rooted if one breaks and they still have another.
