front brake calipers

[orentha@xxxx]

I had my front brake calipers and master cylinder replaced last 
summer. And recently I noticed that my brake pedal doesn't have much 
pressure and goes all the way to the floor.
So I took it in and had the brakes tested. And the bleeder screws in 
the front calipers are completely stripped out.
Is there anything that would cause the screws to be stripped out ?
Or is it just that the mechanic who installed the calipers last 
summer did it??

I'm just curious because it's going to cost me about $250 to fix this 
when I had the exact same thing fixed last summer.

Thanks.
Jim Teston #15314