http://www.swtor.com/de/community/showthread.php?t=357594
check the post by CzaplaM, should be the last one on page 1, he goes over how it "works".
In my experience, After I had waited a full week (7 days) from my last respec, it was free. The NPC may quote a price, but when I committed to it, it actually didn't cost anything.
I have not been able to figure out what the trigger is.
BW claims they're working on fixing it...