I haven't encountered this problem. I just equip my gear and add a new gear set to the list if it's the first time i'm gearing that job. You don't have to set it to a hotbar, can still just change by opening the gear set list on character screen. I've got 2 crafting jobs with the exact same gear right now and no problems.

Actually I did encounter this error one time once I upgraded my ACN book and sold the old one, then tried to switch to SMN and it wouldn't. I just had to manually put the soul gem on and then update the SMN gear set.