Turn off automatic note functions

Yes, I'd say that's a result of your unfamiliarity with the program, although to be sure, you're hardly alone in this.

MuseScore has a a different way of editing music than, say, a word processor does of editing words. It takes a while to get accustomed to, but if its any consolation, virtually everyone who uses both Sibelius and finale will tell you Sibelius is much easier to use, and MuseScore is much more like Sibelius than Finale. I came from Finale and found the adjustment difficult at first, but within a week, I reached a point where I knew I'd never go back.

Anyhow, the simplest way of explaining the difference here is, what would it mean *musically* to delete a rest? You can't hear a rest, so how would deleting the rest change anything? You can't delete silence. MuseScore thinks musically, whereas a more "visual" program would tend to say, deleting a rest should be like deleting a letter in a word processor - everything else just moves over. But this is really backwards *musically* - you're deleting something, and the result is that now suddenly you hear something?

So when you changed the quarter to an eighth, MuseScore assumed that was the *only* change you wanted to make - you didn't also want all the rest of the notes to move over just because you shortened one. That's why it inserted a rest - so the notes you didn't change would not in fact change. And as noted above, deleting a rest really doesn't make musical sense. The only way to not hear a rest is to actually play something instead. So if you want to not hear silence, the way to do that isn't to delete the rest - it's to enter the note you want to hear instead of the silence.

Now, if it so happens that the sound you wanted to hear instead of that silence is the quarter note you originally told MuseScore you wanted to hear on the "and" of 2 but now are changing your mind and wanting to hear right *on* beat 2, then you tell Musescore that *directly*. For instance, by copying and pasting that note (or a whole series of notes you want moved - MuseScore couldn't possibly guess how many notes you want to move) to the location where you have now changed your mind and decided they should start instead of where you originally told MuseScore they should start.

Sounds complicated, I guess, when it's put into words. But it really does come down to this: think musically, not visually, and things start making a lot more sense. If you want to hear a note instead of a rest, simply enter a note in place of the rest - that's all there is to it. If you want change when a note gets played, you copy and paste it to a different location in the measure - that's all there is to it. You don't accomplish either of these tasks by fiddling with what what used to be there and hoping that this has the right magical ripple effect on the notes you actually want to hear - you simply enter or move the notes you want to hear directly.