Depromoted
Where someone is promoted upwards into a worse position than they had before. Unlike a demotion, it is done with a smile and a pat on the back, but with net negative results.
That person was depromoted into handling the payroll system for everyone in the building. Poor guy.
depromotion
When someone is given a promotion so that their boss can get rid of them without having to fire them
That guy given a depromotion and now he is a supervisor because he could not handle doing the work.