setting crescendo / diminuendo lines and hairpins position to below staff doesn't 'survive' save/close/reopen

1. Different dynamics and hairpins are not possible for voices, playback wise (see also #58031: Dynamics/hairpin range for Voice)
2. Different style settings for dynamics and hairpins per staff are not possible, these are per score

It's been that way ever since > not a regression
You can change those dynamics' and harpins' properties to 'Below' via inspector > Workaround

Oops, I see, the (de-)crescendo lines and hairpins don't retain their setings across a safe/close/realoed

I guess this is probably only an issue for scores in which the style default has been changed to above staff (the base default in MuseScore is below). So now if you flip something below, it is probably seen as being the default value and hence not written to the file. We should be setting the UNSTYLED property flag which should make this work. But clearly it doesn't for whatever reason.

so the workaround is to leave them at the default (below, via style) and modify those for voice 1 to above (via inspector)

That should be true, yes. See #281432: Placement of lines set by "X" command lost on save/reload. I think it's this "propertyDelegate" stuff confusing things - some properties belong to the spanner, others to the spannerSegment, and signals get crossed sometimes. Working on a fix.

Turns out that code is fine, the problem is a bit deeper but still simple. In short, we don't fully honor the placement style default for hairpins (or pedal lines, perhaps some other elements too) at all. Sure, it works to have the style default set to "Above" when adding the hairpin via drag&drop or keyboard shortcut, but not on double-click. You can also see this if you hit Ctrl+R on a hairpin - it reverts to below even though above is supposed to be the default. Same for the reset button in the Inspector.

The fix is to make sure propertyDefault returns the correct style value for PLACEMENT for all elements. RIght now it does only for the elements that went out of their way to special case it. I think it's best to address this at the Element level, and that does fix these problems, but I will do more testing to be sure.

https://github.com/musescore/MuseScore/pull/4894

Fixed in branch master, commit ffc17b4f3a

fix #287445, fix #287484, fix #284074: line style issues

Fixed in branch master, commit 1691755b72

_Merge pull request #4894 from MarcSabatella/287445-line-placement-below

fix #287445, fix #287484, fix #284074: line style issues_

Automatically closed -- issue fixed for 2 weeks with no activity.