When you click and hold the block group without releasing with the left mouse button, and then move your cursor to the retry button and you release the left mouse button, the game crashes.
I think "Footsteps", "Preparation", "Snowflake", "Useful White Boxes", "Just White" and "4 Blue Blocks" all could be offical. Possibly some others too.
sound on / off added (burfy's feedback).
16 official levels now. All levels are great. I must say I'm a big fan of Psychotronic's levels (thx Psycho). When a level is "only" accepted, it doesn't mean it will not be official one day, it's just I'm not sure for now.