I know the problem:
I used the 2nd voice -without knowing- later in the score. That’s why happened what happened.
That means every time you DON’T end a voice, there is a risk, you will use it again (if you work without colors) - which causes trouble later…
For starters, your rests were consolidated so it shouldn’t much matter to begin with.
Next, you can start and end voices wherever you want. There’s nothing wrong with using a voice later. Furthermore, it’s quite easy to switch from one voice into another. Just select the notes, right click, and then use the change into voice command.
I never have voice colors on and yet almost every single document I make has at least two voices per stave. As long as you remain cognizant of the fact that there are multiple voices, and you look at the caret, it is very easy to tell what’s going on.