Uplink Balancing don't release the line properly

Hi.

We have three Uplink lines.
One Wan and two other of spare line.
They weight as 100 to WAN and 0 to the others.
Few days ago, my WAN fail and the The other line kicked in as it should.
After a while, the WAN start working again, and all went back to normal.
A day later, I have noticed that the Reserved line, didn't release some users and still active.
Persistence - 5 minutes.

Any Idea?