IRS used to have "temporary" and "permanent part-time" job categories, mostly at the Service Centers.  I'm not sure whether the system still operates that way.  Most of them have full-time supervisors, and some of those have not been on the job for more than a year.  

 According to recent data, around 150,000 federal employees leave the government each year through retirement or quitting.  About 75,000 people took the "quit now, collect a paycheck through September" offer.  So, many of them were probably on their way out the door anyway, and appreciate the going-away gift.  Our tax dollars at work.