Anyway, here's what happens:
When I have all sounds (music + speech + FX) on, I can mute everything by pressing CTRL + U hotkey, and then bring it all back by repeating it. Works fine.
But when I first press CTRL + U to mute, then go to the game menu by pressing ESC, then return to game, and then press CTRL + U to unmute, both music and FX return, but speech does not. It is and remains muted, and can be restored only by going to the sound menu and raising the level up from zero.
Is this how it should work, or is this a bug?
I can repeat this over and over again, so it's not a one time thing.
I am using Windows 10, latest ScummVM Windows release, and Broken Sword download from GOG.