The new editor seems to prefer CSS inline style over font tags for it's own code creation. That's not really any surprise, as most of the modern up-to-date editors tend to avoid obsolete (termed depreciated) code.
I would have to see code examples to run any checks or speculate on why it's dropping fonts and sizes, other than if those were originated from incompatible sources, like Office/Word.
Posting examples is always the best method to get assistance, and to get Auctiva's attention, i.e. giving tham a quick way to replicate a problem.
Danno