Each PQ has it’s own index file and it's version could be different from “global pool”. When pool settings are changed, MDT sends new limits and limit’s file version to OST. OST discards new settings if the version is less than it’s own version.
I.e. if you make 100 limit changes for a user from FOO pool, OSTs file version becomes 100+initial_version. Since this moment OSTs from the FOO pool ignore new “global” limits.
And if the latest limits for a pool FOO were zeroes, these OSTs think the quota is disabled for a user.

Below is a message can be seen if you hit described problem:

qsd_upd_schedule()) lustre-OST0000: discarding glb update from glimpse ver:7 local ver:203