My 93 Grand Cherokee Brakes

I recently replaced the Brakes Master Cylinder(with reservoir). today I was doing routine check and I noticed a spill on top of the reservoir, I removed the cap from the reservoir to the front of vehicle and fluid level was low, then I removed the other cap to the fire wall an the fluid level even out in both compartments of the reservoir,.:cool:Any Ideas why? May be air still in the system even if I bleed it? Thanks