[Milhouse]

This only happens with passthrough and respectively Sync Playback to Display disabled, right?

No.

ION2 into 7.1 Onkyo AVR: passthrough enabled, sync playback to display disabled
NUC into 2.0 channel computer monitor: passthrough disabled, sync playback to display disabled

In both cases there is 2-3 seconds silence after seek (eg. 7-second jump back, you miss the first 2-3 seconds of audio).

I disabled passthrough on the ION2, same result - 2-3 seconds silence after seeking.

I also enabled sync playback to disaply on the ION2, and again had 2-3 seconds silence after seeking (although a few times I tested and had no period of silence, so it may be implicated).

I would also say that since #0910, when seeking (even a few seconds with jump back) there is now a much longer "buffering" delay (even though I'm on a GigE wired connection) and the "buffering" busy circle appears on the screen for 1-2 seconds (showing only 100, ie. no incremental buffering - it's instantly at 100%, and then there's a 1-2 second delay) before video then plays without audio for a few seconds.

With #0909, there is no such buffering delay, and no period of audio silence - seeking is much snappier (ie. instant), and generally just a whole lot better than it is in #0910.