Hi!
The problem I've found is quite particular, but I think I'm in the right topic.
There is a NPC dialogue which pops up outta nowhere at Valor Lakefront (discovered after getting my 8th badge). Actually that could be a dialogue from the guy talking about the black out, but he's not there anymore since I defeated Giratina....so either it's a dialogue which shouldn't exist or a sprite is missing imo ^^
Here's a capture screen :
EDIT : seems the bug happens when I turn to up or down