Password update issue on user profile update

Every time we update a property on the User Object, say I change user's 
Title(custom attribute) and save, the password get's updated in the DB. 

Is this the right behavior? The reason I ask is after about 5 mins the
user 
is unable to login into the site unless we go in and reset the password. 

This is a huge issue for us in production. Any one have any insights?

Also, where can I change the cache setting to 0 so that the changes are 
effective immediately?

Thanks in advance for your help.