My employees have 100xxxx employee id's in Update Profile. Why do they also have an id that starts

Hi.  In Travel & Expense all my employees have 100xxxx (ex. 1009678) employee id's in Travel & Expenses, Manage Employee Information, Update Profile.  I just did a random search by putting a 'G' in the "Employee ID:" field and clicking search.  Why do so many of my employees also have an id or id's that starts with a 'G'?  For example, I have one employee that has the following ids:

1006706

G0002

G6706

(In User Profile, all my employees have the ABC1234 format. So this employee mentioned above has VMT6706 as her oprid.)

We are on 9.1, 8.52.08 tools.

Anybody have an idea why I have these system generated 'G' employee id's??