Furnaces do not give XP when smelting items (as intended). However, smelting the items stores the XP in the furnace, so if you smelta bunch of items and destroy the furnace, it'll drop all the stored XP. I'm like 90% positive this is not intended.
Smelting definitely gives mcmmo Mining exp in the Rising world, which I'm pretty sure is intended. I am however indeed getting exp from a normal furnace and a blast furnace from the smelted items when I break it, not while its smelting however.
