arranging menus – WP rearranges them when i save

Now that my menu structure contains 24 items, the menu editor is behaving strangely. I drag and drop the items into my intended order, and then hit save menu button. WP then takes some number of items that I had placed under another menu item and moves them to the end and makes them top level items.

Also, it does not let me move some items to the intended place. I see the ‘ghost image’ of where it might move it too as I drag an item near my intended place. I move it to very near that intended place, and let go of the mouse button. For some items, it will not ‘park it’ in the intended place, but instead drops it into a different indent level.

Is this a known bug? I have latest release of WP – 4.1. I had this same behaviour with 4.01