Brakes went to floor not sure what fixed it

Got a wierd one here. 2001 gmc jimmy. brake bedal went to the floor, had enough to limp it 2 blocks rather than tow it when there was almost no traffic. There was already a problem in the ABS so instead of fix it I removed it now. Hell of a time to bleed it. New master cylinder under warrenty because every test said bad master. Still hell to bleed. Finally got good pressure and imediately poped a rear brake line. Didn't lose any fluid in the first place. After replacing the rear line bled easy. I just wana know what the origional problem was. Was the rear line seeping enough to lose pressure or was it just the ABS and just hard to bleed? Any input?

More often then not the abs requires a scanner to bleed properly.

Ya got that part no problem. The brakes were fine and suddenly went to the floor with no leaks and the fluid up to level. Fixed now but I am trying to figure out what the origional problem was, why it went to the floor in the first place. was fine all day, stopped in the store and when i took off again there was no brakes.