Okay, I did some more testing.
First, I set "Resume playback using bookmarks" to "Ask", and ticked "Pause video playback when entering Theatre View". So I should have the same settings as you Paul.
I tested both the Back key to pause playback, and the Stop button. I played a video, then played some music, then played the original video again. In each case, playing the file again resulted in me being asked if I wanted to resume, and when I said yes, playback resumed in the correct location. Basically everything worked when I was playing media on my HTPC which is the MC Server.
Steps to reproduce the problem.
1) Play blu-ray rip video of movie ABC and then Stop or Go-Back.
2) Play audio file of XYZ.
3) Play blu-ray rip video of movie ABC.
Expected result: Will be prompted to resume or play movie ABC from the beginning.
Actual result: Movie ABC starts from the beginning.
NOTE: If I play movie ABC and then Stop or Go-Back and then play movie ABC before playing something else I will in fact be prompted to resume or play it from the beginning.
Notes:
0. This lot of testing was on my HTPC, which is also a MC Server, rather than just a stand alone PC. That shouldn't make any difference though. Playing stuff directly on the MC Server is the same as playing on a stand alone PC.
1. I used "Big Hero 6" this time, which is a full BD folder rip.
2. I played Jailbreak by AC/DC.
I tried either leaving the music playing so that it was automatically stopped at step 3, or stopping it before moving on to the next step.
3. I did all the testing in Theatre View, but checked the Bookmark status in Standard View.
I always got the expected result. Every time.
BTW Paul if you pause the movie using Backspace, or any other method, then start playing the movie again without playing anything else in-between, as per your "NOTE" above, MC should not be asking you whether you want to resume or not, as that is just a Pause - Play cycle, and the Bookmark will not come into effect. MC won't need to read the Bookmark again, but will just start playing again from where it was last paused. If you Stopped playback, and then restarted it, MC will ask if you wish to resume, and use the Bookmark if you do.
So, bottom line Paul, I can't replicate your problem.If you do some more testing, check the value of the bookmark after each of your three steps, and when you do, make sure that you refresh the view showing the Bookmark, as sometimes it will not be refreshed as you move between Standard and Theatre Views.
For other users in a Client/Server environment:When I moved between the MC Server and my MC Client, as expected the synchronisation of the Client with the Server was a critical issue. Either the Client had to be opened (or closed and then re-opened) to force synchronisation,
or I had to manually synchronise the Client using the button under Playing Now,
or I had to wait an undetermined time for the Client to automatically synchronise with the server.
Pausing or Stopping playback on the Server, then opening the Client, or synchronising the Client which was already open and playing the same movie, worked every time. The functionality worked in the other direction as well, as long as the Client synchronised back to the Server before starting and resuming playback on the Server.
I saw some issues when going back and forth between the Server and the Client, which I won't document, because I think they were all caused by a lack of synchronisation between the two, or the fact the if you pause playback on the Server, resume and play some more movie on the Client, then go back to the Server and un-pause the movie, it doesn't resume from where the Client finished, because it doesn't read the Bookmark when it is simply resuming a paused movie. It just starts playing again. Very minor corner case, and probably a good reason not to use the Backspace = Pause feature in a Client/Server environment.