Hello. I found two bugs related to music in these two games, and a solution to one of them.

In Contraptions (TIM4), the bug in really minor, but I will mention it anyway. If you go to the preferences and see the "sound test", you can switch between Digital music, Midi music or turn the music off. But if the switch the music back to Digital, the right scroll bar will be inactive. You can exit the preferences and go back in to fix the bug, but switching from None to Digital will trigger it again.

In Even More Contraptions (TIM5), TIM4 bug is fixed, but there is another, more serious one. The Midi music does not work. However, i found the solution. In TIM4, Midi files are stored in the game's main folder. In TIM5, there is a saparate "music" folder with these files. Placing these Midi files in the game's main folder (like in TIM4) will fix the bug.