In the image you'll see 3 91+ board rewards, the first two gave me plenty base and job exp, and the third one (siroma) gave me 1 job exp, either because I was job level 69 at that point, or some strange issue.
Is this as intended? If so, I recommend you change it because it is a bit of a buzzkill when people are excited to reach 3rd class and you find out you need to kill a whole bunch more mobs legitly.