I’ve seen this myself, but I don’t know why Unity does that, I think it’s not very userfriendly. Could you submit a bug (with our mesh attached) and post me case number? I’ll see if we can improve workflow on Unity’s side.
My quick suggestion is: if it’s just a single mesh in a file, then try putting it at (0,0,0) in the modeling tool and set rotation to (0,0,0). See if that helps.
I just wanted to let everyone know that is reading this thread, that I figured it out. In the case of a multi-mesh model, you would have to assign the mesh collider to the specific mesh part not to the whole model.