Steps to reproduce:
-Create a timed assessment with only 1 submission allowed.
-Log in as user and open two tabs, both at the assessment tool home.
-Start the assessment on one of them and wait until time expires.
-While the answers are being sent (a few seconds gap) head on to the other tab and click on the assessment link. It allows the user another submission.
Reproduced on trunk-mysql.nightly.sakaiproject.org server