It sounds like something has incorrectly dumped the songs in your recent apps list. This list is maintained by the OS rather than Start10 which is why reinstalling Start10 did not help.
To reset it, right click on the taskbar and pick properties and then on the start menu tab. In the privacy group untick "Store and display recently opened programs in the Start menu", click apply and then retick it and click apply. Sign out and in and your list should be blank.
If this happens again please let us know what you were doing before hand so we can track down the issue. With Windows 10 being beta it could well be a bug in the current build of the OS.
