It might have been one of those abusable game mechanics or behaviors (like movement that allows bunnyhopping etc) that no one got around fixing. If this is the

It might have been one of those abusable game mechanics or behaviors (like movement that allows bunnyhopping etc) that no one got around fixing. If this is the case it is what I would call a "real" secret - it is not enough to look at the source code, open a map file, or use noclip to crack it, you have to understand how the game works.