I defeated Roark and Kadabra is lvl 17.So why?
The reason why it doesn't listen to you is because in Platinum you need to have 2 gym badges for any other persons Pokemon to obey you only up to level 30
If the Pokemon was traded it may not obey you until you have the next badge. I experienced this glitch in alpha saphire. Im sure next gym it will obey you then. It must be a glitch or maybe if traded the last trainer could have hacked it in.
Hope I helped and answered your question :)