Cleared the app from my MS, rebooted the PSP, put the app back on the MS, started it, now there are no tetris blocks anymore. Wild guess is that this might be a bug in the tetris app though, and probably quite easy to fix.
Also, the app is reporting the date as September 29th for whatever reason, even though my system date is December 14th.
Might not be very important, just reporting what I've found.