Hi there, I have a similar yet complex problem.
On release, I have bought the full DLC pack (Track, Gear, Paint & Cars).
Got all the packs unloaded in GT5 and played with paints, drove with new car on new tracks, ect.
As I play daily, I get a 200% login bonus.
Three days ago, it was reduced to 170%, yet I had played previous day with 200%. Also my online greeting had reset to default and some cars had all their tuning undone ( even chassis stifness and engine tuning).
When I start playing today I can redownload all DLC except track-pack, so now I have all the DLC cars, special paints and outfits twice. But I have also lost the Space Kart track.
Since, I have reinstalled save game, Deleted Game data, reinstalled Game data, reinstalled diff save game ( I have multiple back-up files, 4 from last week).
Nothing worked, I cannot get Space Kart track back.
In PSNstore I cannot open GT5 DLC-page, because entry denied to user, yet everything else opens and i do have sufficient credit in acc to buy stuff.
Have no idea what is happening, but if I find a fix, I will let you know.
Good luck!