Why my slurs keep on moving when I press "R"?

Hi Friends,
I cant not figure this out for the life of me.
When I press R to duplicate the note my slur moves from the next note to the previous one.
is this a bug?

It’s not intentional behaviour that the slur should end up snapping backwards when you repeat a note at this position in the slur, but I’d hesitate to call it a bug. Dorico has to snap slurs whenever you edit notes that are contained within or bound the slur. In this case it doesn’t actually need to change the snapping result, but I’d need to look into it in more detail to tell you exactly what decision it’s making here. I’ve made a note of it and I’ll take a look when I have a bit more time.