Thanks for the fast replies!
The sho log system command is indeed very useful to troubleshoot. I checked the LMS 4 times or so, because I was thinking the same.
We configured the VAP's and system profile on the local controller and when they synced, the master knew it too. We also reloaded the local controller a few times, so the config was definetely saved.
A technician of our vendor did a firmware upgrade on all the controllers and now the AP's aren't unprovisioned anymore... I'll ask him if he did something to solve the problem (I didn't tell him the problem yet). If he didn't do anything, I guess it was a firmware issue. I'll post it here when I get his answer.
Can someone post a step by step setup on how to create a new AP group with existing vap's please? That way we can verify if we didn't forget a setting. (We're not that into wizards, because we want to know everything that gets configured :-) )
Thanks!