All of these are some really interesting mistakes I don't think most of us caught! We have some very observant people on SS.

I'm going to see it.

Yeah, It was wicked awesome.

A really obvious one the whomping willow changed its place

well I am not sure if this is what you are asking but there are stairs

not in a presence of a muggle but harry was the only one in the room

Wow. So many mistakes! You people have good eyes

I kind of noticed that when they went back in time, when Harry and Hermione were trying to save Buckbeak, the time seems a lot longer than when it actually happened.

Well to be honest, I think people who recognise mistakes like that are only because your actually searching every bit of the film for a mistake. I mean the generation fame one for example, that's not what people are supposed to be looking at. Your supposed to be looking at Dudley. So I think people just search for mistakes like that as if life depends on it.

I never noticed them! I'll have to look out for those next time I watch the movie.

when marge is blowing away the wall in the garden keeps getting longer and shorter and changing positions

also at the beginning harry is just doing his homework and he just lighting up his wand not sure if this counts as real magic??

When the present trio are exiting Hagrid's hut before Buckbeak's execution and Hermione hears a noise behind her and says: 'I thought I just saw... nevermind' or something like that. It sounds different to the time when she and Harry go back in time and are hidden in the Forrest.
Also, when Hermione knocks her crystal ball off the table in Divination, you can see a little tube which goes inside the ball which produces the smoke. But when they cut to the shot where Hermione is walking our of the room, the tube has gone.

The movie had plenty of mistakes, but the biggest one was the dark tone. It was jarring, and the darkest movie of the series. It was not loyal to the spirit of the book, as the book was not nearly as dark.