I generated a test mobi in the same version and don't see it (yet).
If I can duplicate it I'll try it again as well after the next release so there's more of us in the wild looking for it
edit: Aha! When I closed Kindle for Desktop and opened it again it installed an update. The updated version showed all the funky characters.. (v1.23.1 50133). I'm not sure what version of Kindle it was before that though. Hope that helps with testing against Kindle after
The thing that confuses me about this one is why kindlegen created a perfectly formatted version from Scrivener when read with the older version of Kindle, and created a messy one when read with the new version.
You'd think if it was happening on the Scrivener side that kindlegen would have made a bad mobi file for both the old and new Kindle.
I just compiled my test file as an epub from Scrivener and it came out fine. Then I opened the command line and ran kindlegen manually to convert the epub to mobi. It reintroduced most of the extra characters during the kindlegen process.