Hiring Manager Calling Current Manager

I recently interviewed for a position and was given the opportunity to have an observation experience as well. The interview and observation both went well.

During the interview the hiring mgr asked if it was okay to contact my current employer, and what my managers name was (for some reason when she printed my application it did not fill). I gave her my managers name, and then the number I had listed on the application was HR.

The hiring mgr emailed me today and stated she was trying to contact my current manager, but that the number I had put on the application was for HR. She wants my manager's direct number. Is this the norm? I was under the impression that they can only call to verify employment length, etc., which they could do through HR.

I don't have anything to hide, but if this new job is not extended to me, I do not want my current mgr to think I am a flight risk. I am uncomfortable having her speak directly w/my current manager, but don't want to miss out on this opportunity.

Any advice would be greatly appreciated! Thanks!