I have the RRS BH55 and never had a problem such as yours. I assume the two ballheads operate similarly from a mechanical perspective. My suggestion is to email RRS and describe your problem to them. They may be able to offer a solution that you can implement on your own, without sending the ballhead back to them. Maybe something is struck in there somewhere?
Thanks for the feedback Alain.
I have a BH-55 also and never experienced something similar with it either... I have been using the BH-40 more recently in order to further reduce weight when I hike with both the Nikon and Ebony.
Something being stuck is also my guess and I will indeed contact the good folks of RRS to see what they can propose.
Thank you again for taking the time to reply.