I have a conundrum. I have a multiclassed 6th Paladin/ 5th Warlock character. With 6 levels of paladin, I have 4/2 spell slots, and as a 5th warlock, I have 2 spells that are cast as a 3rd level slot. The character has the Fiend pact, and therefore I have chosen Fireball as one of the spells in my narrow Warlock spell list.
Under the multiclass section, (and I'm paraphrasing here, without a PHB in hand), that spellcasters can share their spell slots with pact magic, and vice versa. Warlocks are not on the multiclassed caster table.
So, that being said, RAW should mean that I can burn a 1st level Paladin slot to cast a Fireball from my Warlock side, since all spells cast from a 5th level Warlock is done at its highest caster level. That means that I should literally be able to cast eight 8d6 fireballs before a long rest.
I've searched high and low to prove my theory wrong, but I think I'm correct. It seems unbalanced, and if I abuse it, no doubt my DM would intervene. What do you all think, is my logic sound? Is there errata on this loophole?