Why did my sisters get romantic feelings for each other?

This has been happening since 2014. It's really annoying and sometimes quite gross. I thought they said they patched it one time (especially when it happended with kids) but I guess it is one of those things that can't stay fixed. It seems every time there is a new pack or a patch these type of problems reappear over and over. It gets really tiresome to have to put up with screwy programming like this.