I thought it was missing features in the C++ compiler and its less-than-perfectly-clear error messages which led to the split. The C compiler was pretty sound

I thought it was missing features in the C++ compiler and its less-than-perfectly-clear error messages which led to the split. The C compiler was pretty sound early on. Sure, occasionally there were bugs, but users, including Linus Torvalds, complained loudly about those, because expectations were already high.