brake Light On ?

Just had the master clyinder rebuild. It was a old one off a duster I think.
One thing I did notice is that after bleeding the system I pulled the cap off the master cylinder and pumped the brake pedal and a little squirt would come up from the piston on the resivior for the rear brakes every time I pumped the brake pedal. Is that normal?

Maybe the master clyinder is bad after a rebuild? But the pedal feels fine and does not move or react like a worn out master cylinder. Just checked it out with out the engine running.

Chris