Hello. I changed a song from DB key to C key. However, the slur, which should be above and below, is attached to the bottom. Is this a bug? Can I change this in the settings? I used Google Translate. Thank you.
Isn’t it because the stems are flipped, and now the voice bear a different relationship?
You can see that the transposition has changed the stem directions. That’s probably why Dorico resets the slurs to their default position (i.e. both on the same side, since there is only one voice). Select one of them and press F.
It’s not expected, and I can’t reproduce that. Maybe having a look at the file could help, but I’m not sure…
If you select these notes, you’ll probably see that in the properties:
You can switch off the “Accidental” button.
I also followed the method you mentioned. However, I asked because I was curious why that happened. Since Dorico is so smart, I assumed it would handle this situation on its own, but I didn’t quite understand it this time. Thank you.
For what it’s worth, Dorico is not helping very much with those double slurred groups of notes because it seems the norm has changed, and it’s no longer considered needed. One slur is enough, the second one does not add real musical meaning. But if you are trying to reproduce engravings that used that convention, you are going to use F quite a lot 
ex in Gould Behind Bars
Oh. I see. I understand the reason. It seems that only one is supposed to be done. Thank you. I used Google Translate, but the meaning isn’t being conveyed very well. I understand now.
My 2 cents:
The less black you have on the page (without losing any information), the better. It is redundant to show 2 slurs. Showing 2 slurs is spoon-feeding the user to the extreme. Do not insult people’s intelligence. Unless it is difficult to understand the slurring, show only 1 in all versions.
Yes, that’s the today’s norm, but there is a lot (and I mean a LOT) of literature out there where there are two slurs, especially in piano reductions. And when you’re asked to recreate those scores, it’s not always well received when you make those changes. They need to be acknowledged by the “boss”. Same goes with syllabic beaming.
Yes. I understand. Thank you.