There is a bug I found in the most recent 7.0.7 version. When you use the move trick to give a flying type Poke an Iron Ball, it will say that it has fallen to the ground, however ground type moves still will not work.
Every time this happened to me it was after the Poke used U-Turn and then got set back out after, I don't know if that affects it or not but thought I would try to report this bug.
If the Iron Ball is held by your own Poke (I.E. you put it on your own Poke) it will work and ground type moves can hit a flying type Poke, but after using trick for some reason either after they return the Poke and send it back out (which still plays the Iron Ball text) or before that (which I haven't tested yet) the Poke will still be immune to Ground type moves.