I've always played Simutrans-Extended with disable midi. This option is no longer saved. So I had to check this option every time I launched the game. But on the other hand, the Music volume is remembered correctly, so I found that setting the Music volume to 0 could work around this problem.
The disable midi option is not currently saved (or doesn't load properly) anyway.
I declare myself guilty. Here is the fix which should return the previous behaviour https://github.com/jamespetts/simutrans-extended/pull/377
Thank you for this: now incorporated. Apologies for the delay: am currently exceptionally busy in work so do not have time to look into this in any detail.