Joined: 25 Oct 2005
Location: A haunted Castle somewhere in the Bavarian Mountains
Might be a regression in either the DXA playback code or the tools, since, as you already figured out, re-encoded DXA's aren't really needed anymore.
So i guess no one took the time to check for regressions.
This is a guess, i didn't check if it produces said artefacts/glitches on my version