Ground vs. Flying: A Glitch in the System?

[CaptainNikolai 1]

While training my Honchkrow, I ran into a wild Sandslash. I decided to KO it for experience. During the fight, the Sandslash hit my Honchkrow with Dig! As far as I can remember, Ground type attacks aren't supposed to affect Flying type Pokemon. To further test this, I began training my Omanyte. I ran into a wild Zubat, and tried hitting it with a Mud Shot. No effect. So...Something is amiss here?

[JayDo 0]

The only reason it would have hit is if you had used Roost the same turn with your Honchkrow. Since Roost removes the flying type for the remainder of the turn. As far as I know, the ground vs flying type mechanic works fine.

[king42 0]

King42 Research Completed with Results of Pokémons hitting my flying and levitating type pokemons

I actually ran a research on this and I found out that some ground pokemons actually are holding a Iron Ball as an Item. Knowing the extraordinary Iron Ball marvelous ability that cuts the user speed but makes flying type and levitating pokemons venerable to ground moves.

[Woobowiz 0]

King42 Research Completed with Results of Pokémons hitting my flying and levitating type pokemons

I actually ran a research on this and I found out that some ground pokemons actually are holding a Iron Ball as an Item. Knowing the extraordinary Iron Ball marvelous ability that cuts the user speed but makes flying type and levitating pokemons venerable to ground moves.

The only possible explanation is the usage of Roost.

Iron ball gets rid of Ground type immunity to the HOLDER of the item.