I cannot help but feel quite provoced by such a statement, and I can only reply to such a categoric statement with "apparently not".
This is J 2.5.6
This is the menu structure in use for the mobilesite (mobilemenu-structure), I've also tried renaming all aliases in the mobilemenu to globally unique names (no aliases on other menus that matches), with no change
I've attached some snapshots of the menu if I use the standard menu module, as you can see it keeps the toplevel, but the layout is not that good.
First I go to the startpage
Then I click on 'Om klubben' and the submenu appears
Then I click on 'Indmeldelse i klubben'
If I use the mobilemenu module, it shows the problem when clicking on a subitem, as shown below.
First I go to the startpage
Then I click on 'Om klubben' and the submenu appears
Then I click on 'Indmeldelse i klubben', and the toplevel disappears