The dummy demonstrates all upgrades in place, nothing was left... but when I remove the dummy, it's back to just having Pro G/B but no Keys?
The only way this makes sense to me is if we didn't follow the whole delete-and-rebuild-caches part of the process. If you have the dummy there, the game will parse and present that data even if there are older/existing songcache entries for the same songs, but as soon as you delete it, it will revert to the 'first' content added to the cache and then integrate the pro guitar/bass data from the upgrades as it would with a marketplace upgrade.
Pro bass/guitar upgrades can be loaded onto "existing" song cache entries because the game was build to accept those upgrades - it's why the PG/PB customs folks give you pre-made CONs for those upgrades and just have you put them on your USB key. Getting harmonies and keys/pro keys to stick requires much more in the way of manipulation.
I reiterate these fairly often, but in the broadest of brushstrokes, here are the steps you should be taking (the video/guide go into them in detail):
* Delete any existing song cache files.
* Prepare a USB drive for customs and put TU4 (or TU5 - whichever one is also on your Xbox HDD), the dummy package, and the upgrade package on it.
* Remove your existing DLC (the songs you want to upgrade) from the environment (disconnect hard drive, move song files to a *different* USB key and disconnect the USB, etc.).
* Connect the RBHP USB key.
* Boot up the game.
* Build your song cache and save it on the RBHP USB key.
* Power down the console.
* Reintroduce your DLC (reconnect hard drive, reconnect the DLC USB, etc.).
* Boot up the game.
* Let it add all your DLC files to the song cache.
* Quit to the Dashboard.
* Delete the dummy RBHP file (not the upgrade file).
* Boot the game.
Pro guitar/bass (and pro drums, actually) don't require these - they just need the RBHP USB and need you to plug it in - but the other upgrades will not work without going through all of these steps.