From a post on aq2world:
The "UREMOVE OLDNUM != NEWNUM" is caused by r1q2ded cutting off the packetentities early. Basically there are too many entities or too much activity in one area of the map, and the packet sent to your client would have been greater than the maximum size allowed. When this happens with normal q2 server, the packet is dropped and your client will experience "freezing" where you don't appear to be moving but in reality you are, you don't see any other entities, etc...
r1q2ded cuts off the packet before it's full and sends what it has anyway in order to avoid this freezing effect. However some clients will print the "UREMOVE OLDNUM != NEWNUM" warning since they are expecting data to be there when it is not. This is a fairly harmless warning and can be fixed by using a client that hides it Smile.
Occasionally though during very heavy activity, some important entitiy updates will be lost and you will begin to see strange artifacts such as teleporter trails on players, flying gibs, etc. To fix this, simply exit and re-enter the area of the map where the problem is if possible.
I'll probably look into disabling this feature by default so that admins know that enabling it may cause such warnings or other problems.
The say/qconsole.log sounds like a good idea, I'll add it to the next version.