Speculation about bugs:
From my reading of the code the kpd_coalition_dissent can go up even if you're not in a coalition with them. Also if you are in a popular front or left front coalition and then have an election, geting in to a coalition with KPD should not risk a civil war anymore, since it's already been done.
From my reading of the code you will still be able to get negative unemployment.
From my reading of the code you will still be able to get negative support in the military if you block the building of the ship.
Normal bugs:
If you hold an election before Müller dies you can choose Breitschid as Chanselor.
Sometimes you cannot adopt an economic policy when you should be able to. I have no clue why, I saved on the crisis screen with WTB support being 2 and saved. Modified it several times and tried over and over again and it just did not accept it. Not when I had 4 not 3 not 2. Then I loaded to an earlier save made no memorably different actions and it accepted the plan.