[Users] 2 Openser Instances

Have anyone tried running 2 separate instances on OpenSER (running on different ports) ? Both these instances are doing almost exactly the same thing, they take in REGISTER and save them into the locations database. They all do all the other processing like INVITE. Will this causes a problem in MYSQL ? I'm asking this because i got a very strange problem. I register 1 UA to each instances. When i did a ul show , it always only have either the UA from instance A or UA from instance B . Note, these 2 UA have different numbers. Why can't it just save both into the MYSQL DB ? I would be glad to clarify any doubts. Please assist as far as you can. Thanks! Regards, Sam