Enable “Keep selections while typing in multiple selections”.

xx oo
oo xx

Select all “xx” (or “oo”, to see different result).
(Press Esc once, to see different result.)
Press Enter (or use “Insert CR/LF/CR+LF” command) 2+ times.
** Extra spaces appear in the selections.
** And note the difference (in length of selection) when using “Insert CR+LF” command.

You use “CR+LF” in other places. So how about also changing the “Insert CR and LF” command name?

Make multiple selections.
Type a letter.
Undo. (The multiple selections persist.)
Switch to another wrap mode.
** The multiple selections are canceled.
(Redo doesn’t has the issue.)

Make 2 selections in the same line.
Use Shift+Left/Right to extend the selections.
** The 1st selection will collapse once either cursor goes into the other selection.
In UltraEdit, they merge as one. But I don’t see why/when we should use it this way.
I think an “ideal” fix (if possible) could be: Prevent the cursor from moving any further once it touches the neighbor selection, in order to keep the existing selections individual, in case one still wants to change them (e.g. move the cursors back).

In UltraEdit, Ctrl+Click can remove a 0-width point when in multiple-selection/point mode.
** In EmEditor, I have to extend it before removing it. (Though “Deselect Top/Bottom Selection from Multiple Selections” command doesn’t has the issue.)

+ Suggestion 3:
In UltraEdit, Left/Right key also can be used to move the multiple cursors among the lines. (Shift+←↑↓→ to extend multiple selections)
Actually, in UltraEdit, every cursor in multiple-cursor mode behaves unconfinedly and naturally, just as the single cursor.

Issue 5:+
Select All Occurrences.
Press Home (or End).
Pressing Backspace (or Del) key does nothing, but is added into the Undo history.