Oh2 und oh3 parallel

Hi everyone,
i am running OH2.5.7 on an Windows System. i am just fine with that.
now i wanted to have a look to the OH3 and decided before i install it for good,
to run it parallel to get an idea of the system. so i took a raspberry an installed it.
so far so good, no problems.
then i installed the first binding, in my case the Homematic. no problems. but after
a couple of minutes the oh2 system didnt work with the homematic stuff. so i turned the
raspberry off an started oh2 new on den windows system and everything was fine again.

any idea why it boarders my oh2 system if the homematic runs parallel on oh3 ?
can i avoid that ?