some people at NeoGAF have encountered a game breaking bug in SS.
here's a quote from the thread other there:
It's been discussed once on our forums when someone encountered the bug, but now it seems to spread pretty much everywhere. There is a game breaking bug in Skyward Sword that causes the game to not trigger an event during the Song of the Hero quest, which prevents you from finishing the game and forces you to start anew.
The bug can occur with either the Faron or Eldin part of the quests. If you do the Thunder Dragon first, there is a chance the events at the Sealed Grounds and Eldin Volcano won't trigger at all.
It's unclear why the issue occurs, and the only knows prerequisite is that you do the Thunder Dragon at Lanayru first.
It might not be a bug that occurs 100% of the time. But it's pretty late in the game (almost at the end) and it sucks to have to restart a new game after 25-30 hours. I tried to reproduced the bug myself using a backup save file but it didn't occurred.
If you encountered the bug and have any info, please share them.
so, basically, nintendo was so focused on stopping Sequece Breaks that they let a nasty bug that actually affects casual players past the final testing phase and now people are going to shit bricks in the last segments of the game until the cause of the glitch is found.
it would be good if someone here encountered the glitch and found a way to solve it. SBing solved the cannon glitch in TP after all.