Inspired by this answer http://rpg.stackexchange.com/a/46442/3799

>Sorc 19/Cleric 1 has a bit more issues. You only have the few L1 cleric spells, and lots of Sorcerer spells, make sure you took cleric spells that scale (so you can cast them in your higher level spell slots).

It is my understanding of 5E multiclassing that you can't cross over the spell lists from one class into the other. Am I mixed up? Is there something in either the cleric or sorcerer classes that allows this?