HIRO kun: The reason for this is that the spell recovery speed in resting is determined by their initial job.
That's one of the many ugly mechanics in Wizardry 6-7 that make me not want to play these games, to be honest. The "base miss chance" mechanic is another one.
(Also, the term used in these games I'm pretty sure is "class", not "job".)
I also don't like how Wizardry 6 took away the ability to go back to town to rest, recruit new characters, and change your party composition.