Just a list of a few bugs I know that exist in Rev 4 and fixes I know for them.
You can use Cheat Engine to log any character in a Rev 4 server. Doing this you can steal peoples items, duplicate items or even crash the server. A fix can be found here. viewtopic.php?f=18&t=5965.
The command /warning can crash the server. it is useless and should just be removed from your server. You can crash the server but using certain symbols in the comment. Example: /warning Elyntra qazw'.
Selling to NPCs. The default value is 40% back on the items stb price. Dura, refine, appraise and gems also affect this price but I don't know the exact changes needed to fix those.
Repairing items doesn't use zulie.
Refining items doesn't use zulie.
PvP randomly being enabled on non PvP maps (Name isn't red).
Summons spawning as enemy. Whoever coded it i rev 4 did something wrong. Review the code in rev 2 for the fix.
Item Mall hasn't been coded properly. It is possible to have more than 2 pages of items.
Lucky Spin crashes when it lands on a blank spot.
Set stats haven't been coded in the server.
Server doesn't read item requirements. Simply editing the client allows you to use any item.