The problem is that the game does not recognise that warlock spellslots are different from the normal ones. This leads to such problems that you can't decide which slot I want to use. With me (2 level warlock and 2 level sorcerer) I can only use my warlock spellslots when my sorcerers are used up. At least when I want to use sorcerer spells. But according to the DnD rules, that is not really the case.
Hope that there is still a patch for this week comes