Locking TACACS accounts

I'm working on an account that uses TACACS+ for access to their network devices.  Our TACACS server is set to lock an account after 3 failed login attempts, which is how it works on the cisco and hp devices, but on all of the fortinet devices the TACACS accounts get locked with only 1 failed attmept.  So my question is, do the fortinet devices send multiple auth requests at once, and if so is there any way to stop this?