I mean almost the first thing that happened to me when I tried to use commercial stats software was being unable to reproduce a calculation manually. Eventually

I mean almost the first thing that happened to me when I tried to use commercial stats software was being unable to reproduce a calculation manually. Eventually found out they had a known bug in their code that was left in for ~20 years and when they fixed it they called it the "enhanced version". The calculation was based on the original version of a paper that was retracted and corrected. I would never trust commercial stats software after that. I really mean this was close to the very first thing, so I would assume it has to be very common.