MDL workspace missing menu items
The MDL workspace changes a number of UI settings, which is not a very popular decision, but in one respect at least it's an outright bug: menu items added since the workspace was created are misplaced. So in particular, Edit / Paste Half Duration and Edit / Paste Double Duration are missing. There may be other changes, not sure.
Really, it would be best to simply remove the menu from the MDL workspace customization. But if it is kept, it needs to be updated for each MuseScore release to avoid missing important changes.