I just rewatched it, and it's a simple enough fix. Just have the tail of a laser blast hitting the wall just as the explosion is happening next to the door way and you've corrected it. Otherwise, I'm not sure why it would explode on Vader, and then shoot an invisible something at the wall, that would explode too.

And the window thing, are we talking about how you can see out the windows behind the 'group' when they walk up, and then can't in every other shot?

If so, how could you possibly miss it? I mean, you had to add the CGI to the original shot for the SEs. When you DIDN'T add it to everything else, wouldn't you begin to wonder?