Hi Laurent,
As you've discovered, OLA is pretty strict about what it will accept. It's designed this way so people discover problems early. That said, there was a bug where the discovery process wouldn't restart if it hit the case you described. That's now fixed in the git repo and the fix will be out with 0.8.22 in a few days.
If you find any other problems do let us know. If it's an OLA specific problem then your best bet is to ask on
https://groups.google.com/group/open-lighting since you'll get a faster response time.
Simon