Manage submissions rejudging is not idempotent

[xiaowuc1]

Reproduction steps:

1. Rejudge some submissions via a manage submissions page.
2. Rejudge them again while some submissions are in QU state.

Expected result:

1. QU subs stay in QU
2. non-QU subs become QU

Actual result:

1. [correct behavior about non-QU subs]
2. QU subs become IE, with a further side-effect that new QU subs are automatically IE