Although there is a big bug with the FMS when it loses the end of the route or has not T/D, I have never had it change like that.

It sounds to me like you went to the DEP/ARR page and because you were still close to KDEN, so the list of arrivals you saw was for KDEN, not for KSLC.

When you go to DEP/ARR page after activating a route, it will always offer the ARR of your departure airport for a while (I do not know the exact time/distance). So when you open the DEP/ARR page, return to the DEP/ARR INDEX page and select <ARR (LSK2R) beside KSLC.