Not sure if this is a bug or not, but I had Hindenburg as President + Braun as chancellor in January '33 with a Grand Coalition; the DVP called a vote of no confidence and I didn't have the resources to assuage them; and the camarilla installed Hitler as chancellor. This was my first playthrough with the camarilla overthrowing an SPD chancellor to get Hitler; normally if there isn't a Prussian coup in '32 and SPD is in power, I've been safe.
Either way, I can't begin to say how much I love this game!