Agreed, this makes the game completely unplayable for me. What were some of the cirumstances surrounding your bug? My party was in Act 2 and I had just got my final companion character. I've tried loading multiple saves (regular, auto, and quick) but all of the above have broken quest log. I happened to have a companion character on a stronghold mission and hadn't claimed the reward yet, and I've seen some bugs regarding the stronghold UI dates being wrong, I'm not sure if the two are connected or not.
I've done no modding or altering of the game files whatsoever in an attempt to fix previous bugs.