When you have a Job, you have a 20 minute cooldown to switch. (I think thats a good idea)

But you can employ yourself, but still have the same cooldown.

Say you want to level with building for the next 20 minutes. So you click on the builder. Now you have the job.

now you accidentally press left click again, or you press space by accident. Now you don't have a job, need to wait 20 minutes, and can't level.

This happens all the time to me. I probably have spent more minutes waiting, to choose my job because of that, than actually leveling.