I just noticed that my machine user name and password are on display above the commit dialog. Since this job site uses single sign on for everything, that's my username and password for the entire system here.
I have three different repos loaded in Sourcetree. Because of single sign on, that is also my user name and password for the one of the repos. The other two are hosted on Github and use an SSH key. However, switching between repos doesn't affect the display of my user credentials.
I don't remember seeing this before. The only thing I can think of that might have changed something is my password is about to auto-expire on the system. Yesterday I set a new password. Today I started up Sourcetree for the first time after setting a new password and had to re-enter my credentials for the company repo.