This may be a struct thing I don't have any older clients to test this on, but when swimming or using /flymode if you target something the game tries to force you at the same Y coord as that target, it stays this way until you log off, zone or die. If you target something else it will force you to that target's Y so it's a pain to swim. (on client 1199)

I have noticed this on the DB project, haven't noticed it on my server but don't swim or fly much on my server, will try to reproduce this on my server and figure out when this started.

Committed a possible fix for this issue, the best way I have found to reproduce this to log in two clients group them and do /follow on one of them then break follow and go swimming / flying and target something and you will be locked to the same y axis, that method failed to reproduce it after the changes.

Let me know if you see this happen again.

Nice jab, I'll watch for this next time I'm on