This is secondhand information, but should at least be comforting to the people following this bug:
http://www.reddit.com/r/mindcrack/comments/1j224u/uhc_xii_episode_6/cbac5ad
TL;DR: This bug basically ruined the Mindcrack Ultrahardcore event, and a prominent youtuber sent it to DInnerbone, who is now aware of the extent of the bug.
The 0.9.1 update resolved this issue for me! Thanks, Grum!
You can select the version of minecraft from the Profiles tab now. The drop down on the main screen is for selecting the profiles.
That said, I have the same not launching issue (see MCL-413) on Mac.
This is secondhand information, but should at least be comforting to the people following this bug:
http://www.reddit.com/r/mindcrack/comments/1j224u/uhc_xii_episode_6/cbac5ad
TL;DR: This bug basically ruined the Mindcrack Ultrahardcore event, and a prominent youtuber sent it to DInnerbone, who is now aware of the extent of the bug.