There have been other mentions of this issue on the forum, but no bug logged and no SQL Developer Exchange feature requests added for it. Here are some found when searching for shortcut: Keystrokes for code folding feature? Mostly they don't work on Mac OS X 30EA2 - Bugs? Collapse/Expand Shortcut-Keys
Others when searching for expand or collapse (general code folding functionality, not necessarily related to shortcut keys): PL/SQL code "collapse" functionality Re: collapse/expand of indented source lines
So code folding issues tend to get addressed, but not expand/collapse shortcut key issues. Perhaps there are different code paths with regard to source files, worksheets, code editors, etc., so it is not trivial. I have seen a case with Source Reformat where one shortcut works and another does not. The Shortcut preferences categorize the various expand/collapse types (All/Doc/Method) as Source, but I cannot any area of the product where they work. If this is a hot button issue for you, I would recommend adding a feature request on the SQL Developer Exchange to see if this gets any traction.
SQL Developer Team