This is a regression, unless I miss something. Such an accelerator used to read <i>.
Consider running the attached code where is done:

KeyCombination acceleratorKeyComboA = KeyCombination.keyCombination("Shortcut+4");
KeyCodeCombination acceleratorKeyComboC = new KeyCodeCombination(KeyCode.DIGIT4, KeyCombination.ALT_DOWN, KeyCombination.CONTROL_DOWN);

In the menu I read "Ctrl + DIGIT4" in place of expected "Ctrl + 4" for the first one and "Ctrl + Alt + DIGIT4" in place of "Ctrl + Alt + 4" for the second.
This issue affects Mac as well as Windows.