I can reliably replicate this problem on my warlock. The issue is minimal in the normal game world, in raids and BGs it is at its peak.
How to replicate:
Join a battleground. You may or may not get a 5 sec freeze up here.
Mount. Then dismount. You WILL freeze up for atleast 3-5 seconds.
Mount again. Dismount. No freeze up. Can repeat as many times as you like, no freeze up from here on.
Hellfire yourself to death.
Spawn at graveyard. You WILL freeze up for 3-5 seconds.
Mount. Dismount. You WILL freeze up for 3-5 seconds.
Activate fel domination. Summon minion. You WILL freeze up for 3-5 seconds.
Hellfire youself to death. Let the freezing start again.
I'm pretty sure it's easy to see the pattern from here on.
I've tested this on Ag_unitframes, Pitbull and Xperl, they all give the same results. Only one unit frame mod I've tested with does not give these freeze ups and thats Stellar Unitframes.
Would love to see this get fixed, can't play with ag_unitframes ( atm ^^ ) and can't play without it.