Brake Padal soft on a 99 Acura CL/Honda Accord

Hello,

I have a 99 Acura CL, same as a 99 Accord with ABS in terms of the brake master cylinder. I just had my rear left caliper and rear pads changed. Now, my brake pedal is hard on the first push, then sloooowly goes down. I went back to the mechanic, he bled the system a bit more, it's a bit better but still doing the same thing. He said he checked for leaks everywhere, couldn't see anything. He said it's most likely the brake master cylinder. Is it possible the system wasn't bled well enough?

Do you agree and thank you.