Grid control 10g

The last two days I have been busy installing and upgrading Grid control 10g.
Because of problems wth an older version of OEM 10g , we decided to install a new version (10gr2).
On a new dell server I installed Oracle Enterprise Linux release 4 (update 6). After installing linux, I started the 10.2.0.1 Grid install.
Next step was the 10.2.0.3 upgrade of the oms and agent. I also decided to upgrade the database itself, which is default 10.1.0.4 (even after the 10.2.0.3 upgrade...)
Before upgrading the database, I tested the Grid control. Everything worked fine. Stopped and started the oms/agents a few time to check stability. No problems so far.
I started the upgrade, which means I first had to install the 10.2.0.1 Oracle software in a new $ORACLE_HOME. After this fresh install, upgrade the new ORACLE_HOME to 10.2.03. When the software is patched to the desired level, use the dbua from your new home to upgrade the excisting 10.1.0.4 database. At this point, some problems occured.
At first the dbua could not perform any OEM configuration ?? Checking the logfile only told me to try this manually...so I did. Oke, the configuration ended without errors, so lets try to start things up.
I started up the oms, no problems. Next, I started the agent....
Seems the agent would not start, the http server could not be started ? Does thsi has anything to do with my database upgrade ??? I can't see how ?
The logfiles showed me there was a port conflict. Suddenly the agent http server wants to use the same port as the oms http server ? Before the upgrade the could work together without a problem, but suddenly they are fighting over the same 6102 port....
The problem was fixed easy, I just changed the local port in the /oem/oemprd01/oms10g/opmn/conf/opmn.xml file.
After this change, the startup succeeded.
But I still don't understand why this port conflict arrived after the database upgrade ?