This doesn't seem to be a very busy forum but I thought it might be an idea to create a thread for people to talk about the glitches in this game as other site I have used are all reporting some. 
 
I found a glitch in the library where I thought there was supposed to be a gold brick (detector arrow showing) but when I turned off the Hogwarts Crest Detector extra the arrow went away so i knew it wasn't a gold brick. 
 
Anyone found any others?

 - Multiple cut scenes not unlocking despite being story related (doesn't hurt %) [Especially cut scenes #64 and #65]
-Cure: None - must make a new save file game if you want it to appear completely. But you can still attain 100%.
-Preventative Measure: Exit mid story. Always wait until the game gives you the option of Continue Story or The Leaky Cauldron.

*- Eelops Owl Emporium Gold Brick Invisible (doesn't hurt %) [it WILL award you. But the sweeping is very picky!]
- Cure: None known
- Preventative Measure: None known

*- Eelops Owl Emporium Sweeeper Disappears (hurts %) [Sometimes if you build the sweeper and DON'T attempt the gold brick your sweeper will disappear]
- Cure: Leigh1997 reports that after replaying level 1-1 and then going in and out and back in to the store will make it reappear (not confirmed)
- Preventative Measure: Get the Gold Brick as soon as you build it

*- Multiple Characters not available for purchase after unlocking (hurts %)
- Cure: None known - must make a new save file game.
- Preventative Measure: Possibly an issue with saving and exiting at an inappropriate time. No one knows yet.

*- Tom Riddle's Diary Not Completed (hurts %)
- Cure: None known - must make a new save file game.
- Preventative Measure: Do NOT quit the game once this level's first cut scene has started! Wait until you complete it. Take note that this level is the next one after CRABBLE AND GOYLE. So maybe do both those levels in one sitting!

*- Polyjuice Potion Not Unlockable (hurts %) [Caused by playing multiplayer when doing the lesson]
- Cure: None known - must make a new save file game.
- Preventative Measure: Don't play the lesson in Multiplayer. Also avoid exiting once you have started.
- Note: WhoDaFoo4 reports that watching the cut scene of this lesson then continuing story makes you appear in the classroom as if you were up to that in the story. However, there is no way to exit and results in requiring you to create a new save file game to get out/start over.

*- Clock Tower Gold Brick Glitch (hurts %) [No reward for completing a required task]
- Cure: None known - must make a new save file game.
- Preventative Measure: Make sure you are aware that this is a glitch area. Put the purple cog on the gears. If not rewarded restart the console and try again using a different method (maybe snake first or snake last). Also try not to collect the characters until you get this gold brick.

*- Dungeon Dragon Exit Glitch (hurts %)
- Cure: None known - must make a new save file game.
- Preventative Measure: RadiantViper suggests waiting for the game to autosave completely before exiting.

*- Camera aims away from reticule when trying to hit a target slightly off screen (doesn't hurt %)
- Cure: You must exit the game and go to the Dashboard. Make your Y Axis style normal instead of inverted. Dark Ryder reports a further glitch with this regarding having made your Y Axis type Inverted and then installing the new NXE Dashboard. If you did this, the Dashboard will say your Y Axis is Normal when it is actually Inverted. To fix this, they suggest exiting HP and making the axis Inverted (Normal) and launching the game again. Then quit out of it and change the axis to Normal (should now really be normal).
Preventative Measure: As above.

*- Gold Brick Locator Suggests Brick in Library (doesn't hurt %)
- Cure: None - ignore the marker
- Preventative Measure: As above.

*- Disappearing Pixies [leaves their item suspended and uninteractable] (potentially can hurt %)
- Cure: None known
- Preventative Measure: None known

*- Both characters fall under the control of the player with split screen (doesn't hurt %)
- Cure: Restart
- Preventative Measure: As above.     
 - Collecting two collectables at the same time causes one to be invisible or disappear (doesn't hurt %)
- Cure: Restart and a disappearing one will reappear. If it was just invisible, just walk over the area it was again.
- Preventative Measure: Try and walk slowly towards two collectable that are on top of or close to each other.

*- Lego Building Areas (Purple Bases/Coloured Blocks) Various Glitches (potentially can hurt %)
- Cure: If within a level, you could try a restart of it - beware levels that glitch, though. If in Hogwarts, move the bricks that aren't stuck and sometimes the other will free up.
- Preventative Measure: Just be careful with these. They are fussy.

*- Starting a Free Play Level causes an endless death cycle [only happens after the last spell lesson with Professor McGonigal.
- Cure: Finish the lesson first (Continue Story)
- Preventative Measure: Finish lessons once you start them without quitting.

*- After obtaining 200 Gold Bricks and entering Borgin and Burkes to play the bonus levels some people cannot exit/return to Hogwarts [appear in Knockturn Alley instead] (hurts %)
- Cure: None known (note: despite popular belief - playing a level as Replay Story will not fix this!)
- Preventative Measure: Make these bonuses your FINAL task in the game. Don't unlock Voldemort if you want to play them before they are the last task.

*- Ghost Guide leads you on a path with an obstacle (usually the troll) [doesn't hurt %]
- Cure: There will always be another way around. The Ghost is taking the quickest route. 
- Preventative Measure: This is again caused by quitting during the story. I am not sure at which specific point, though.

*- Random game lockups/freezes (doesn't hurt % - potentially can if happens in a level that causes one of the above glitches)
- Cure: Install game to hard drive before playing (will remove most lockups but not all)
- Preventative Measure: As above.

*- Not being rewarded with an achievement for a collectable completion (SIP/Gold Bricks/Red Bricks/etc.) [doesn't hurt %]
- Cure: Play a level in Free Play (can exit and save manually after collecting a stud)
- Preventative Measure: As above.