Master cylinder leaking

If you've still got air in the brakes,, it can cause a violent return of fluid to the reservoir when you release the brakes..

To check for air, set the emergency, and with the M/C cap on,, have someone pump the brakes twice,, and hold,, remove the M/C cover,, and have the brakes released..
If you have a fountain of fluid returned,, that's trapped compressed air "springing" fluid back at you.., and that system needs more bleeding..

Brake fluid is excellent paint remover,, avoid getting any on the paint,, if you do,, rinse with lotsa water IMMEDIATELY..

hope it helps