Sync doesn’t do this by default (I haven’t changed any settings to this effect). I’m currently in settings now looking for a setting to change just to see.

Edit: Under settings there is an option for setting comment views (settings/comment options/comment views). However it defaults to new. Additionally it does the same thing in my bed browser using Alexandrite.

The point is though this doesn’t work for everyone using Lemmy and it’s definitely a carry-over habit from reddit and similar messageboard style sites.