Yeah. It's a bit counterintuitive and an oversight by the original developer. It's fixed by
my "fixed" version (which was mostly a technical rewrite).
Three years later, I'm struggling to make sense of why it occurs in the base version of the game. In theory it shouldn't - but I can see I fixed code for the very reason you're having problems and how it could theoretically happen, even if those circumstances look impossible right now.
Under very specific circumstances, you can end up where mom isn't sad (she can become sad for two reasons, one in ch12 and another in ch13) but you also aren't due to go on a date with her either. Because of the way things are checked, because mom isn't sad - the phone call comes from Jennifer. But because you aren't due to go on a date with Mom, the game doesn't offer you the choice to pick between Mom and Jennifer.
Logic says that should mean you should go see Jennifer. (She's calling and you don't have other plans).
Instead, the code effectively "falls" into the "Mom Date" code - and things process down that route.
Right now, the easiest way I can see it happening is if you've been into the game console and set
momsad
to
False
after you decided not to go on a date with mom. But most players wouldn't do that. I'd like to blame some buggy code that was corrected later - but realistically, the chances that you might be loading a broken save file from over 3 years ago while playing the current version of the game seems incredibly unlikely.
Honestly, the whole "mom sad" thing was originally all over the place and cause numerous bugs like this. I was tearing my hair out about it for two and a half chapters trying to bring it back under control with my alternate version.