The SWW 2019 Top Ten list was topped by this idea from Dwight Livingston:
There was a lot of discussion around this while voting was open, but we struggled to define exactly what the problem was. Dwight and I met at SWW and went through an example, however in that case the unexpected mate flipping only occurred in SW2016 and earlier, so would appear to have been a bug that got fixed in SW2017.
However, this idea has clearly resonated with a lot of you, so I didn't want to leave it there as all those votes suggested that something still wasn't right. Dwight got back to me again recently and I think he's found a great example where SOLIDWORKS attempts to realign existing mates instead of changing the alignment of the mate currently being edited.
Have a look at the GIF below, where I edit a mate and change one selection from a plane to a face. SOLIDWORKS currently does not automatically change the Mate Alignment of the mate being edited, even if the normal directions of the old vs new selection has flipped; instead it attempts to flip other existing mates to avoid a mate error. Especially for those who voted in the top ten, does this describe the problem you wanted us to solve?