It's not the fact that you flipped the mesh - you probably need to set up an entitybox (for collision type 3), but ultimately it will be the fact that you're moving the object that is supposed to be collided against which screws you. The built-in collision system doesn't cope with that sort of thing.
Collisions With A Flipped Cube
Blitz3D Forums/Blitz3D Beginners Area/Collisions With A Flipped CubeThe forum is locked. These are the original blitzbasic.com forums, kept so they can still be read. No new topics, replies or edits can be made here. To join in, head over to the Blitz3D+ forums.