Department Number auto-populating in place of Job Number

I notice when we are working in an area where a Job Number should be entered, such as WIP, the default that auto-populates is the Department number.  Of course this will not save as it is not a Job number and will generate an error message.

So, why does it auto-populate to something that isn't even a Job number?  In fact, why is it auto-populating at all?