Redmine

I'm facing a redmine problem as following:
I logged on redmine by my account and do some actions (as show repository or show diff from repository, etc), sometime, it took long time to complete showing then my account had been changed by another one (having 50 users using redmine)so that it will be major problem about security if someone auto has my account (admin).

this problem sometime occurs so that i can't debug to find root cause.

Could you give me some comment about this?

Thank
Nhanntit