If you don't have the hi-res installed, it doesn't matter if you chose 1024... It's 512 in all but name.
The reason you INSTALL it in the first place, is so that choosing "1024" actually does something. WIthout it, 1024 does nothing. It's not enabled.
So, you were really running at 512 before that. Just go back to 512 in the drop box and it'll be back to normal.