It's a bug in the map. The speed is set too high (can't go much over 300). Because velocities are compressed over the network into 2 bytes per axis, the speed ends up exceeding what can be stored there and wrapping back around into negative numbers (or smaller positive numbers - I guess it depends on the compiler settings). You could fix it with an ent file, but the whole map looks pretty buggy, so it's probably not worth it. Wouldn't take long to rebuild the map correctly from scratch.
I could put in a limit for player velocities to ensure the wrap around doesn't happen, but this may have undesired side effects. The jump pads on that map would probably also behave differently than they do now.