http://www.theregister.co.uk/2015/07/29/windows_10_bug_alert_start_menu_breaks_512_entries/
Whoopsie...
Not sure if you need to be a pathological app hoarder to encounter this, or if MS eats up a significant chunk of those 512 entries for their own.
Start menu shortcuts are still shortcut files placed in the same special locations as previous versions of Windows, but the Start menu app appears to be driven by a database on which some optimistic Microsoft coder has placed a limit of 512 entries.
Whoopsie...
Not sure if you need to be a pathological app hoarder to encounter this, or if MS eats up a significant chunk of those 512 entries for their own.