If you are referring to it not shutting down a type changing ability, like with Kudo, Ashaya, or Magus of the Moon, then that is not a bug. The abilities ARE lost, but not before they are applied. The game goes through a series of layers when applying continuous effects, and type changes, which happen in layer 4 come before ability gaining and losing in layer 6. And due to the specific rule 613.6, any additianl effects those type changing abilities have, even the ones in later layers like power/toughness modifications in the various sublayers of layer 7, will also still happen.

In short, ability losing effects can't stop type changing abilities.