I also have this problem or something similar. If I castle, on the app I get the king and rook are in both before and after castling positions, resulting in 3 rooks and 2 kings on some games. The main site doesnt seem to be affected and so I assume this is a buggy app. Unfortunately I doubt very much that this is the place to report the bug. Next stop the iTunes store to look for a "report bug" button......
iPhone Castling Bug

Cheers Rob. I have tried reporting it everywhere I can think of but never get a response. Will keep trying...

When the latest app update was released, did you install it over the one on your device ? or did you close the app, completely un-install, then install the new app ?
Have you tried closing the app, completely un-installing and re-installing (not just installing over the previous one)
Can you please try removing the app from your device, remove the app from your iTunes, then sync the device then search chess.com and re-install the app
If then, you're still seeing this issue on your games, can you let me know which games are affected by this please and i'll take a look for you

I have deleted it, reinstalled it, and it still has this problem. I did this today and all my app updates are up to date.
An example of a game where it is doing this is my game with RobertM1 (1692) and robredwine (1580) which is on move 6 - I have 2 kings and 3 rooks on the ipad game - and it is unplayable on that platform as a result.
It's a bit annoying as I am about to go on holiday and it looks like I'll have to take vacation rather than carry on playing my games whilst away as some of them are unplayable on the ipad.
Edit - I've just seen your comment about removing it from iTunes as well - I'll have a go at that and report back
Edit - no - removed it from iTunes, reinstalled it, etc, still the problem is there. The version in iTunes I downloaded was 13 June 2011, version 1.52 - presumably there isnt a newer version anywhere?

I have also a castling issue: i am in a 960 game. I can castle in the game itself, but NOT on the analysis board. I try to castle queenside by tapping the king and rook. In this particular 960 game, it should result in the king and rook switching places.
The FEN is "n1rkr1bq/3p1p1p/ppnp2pb/3N4/2p2P2/6P1/PPPNP2P/2RKRBBQ w ECec - 1 10"
I don't know if this bug was fixed at any stage, but 3 years on and I've just seen something similar: http://www.chess.com/forum/view/help-support/ios-tactics-trainer-bug-extra-rook
Has anyone else noticed a serious issue with the current version of the chess.com iPhone app? I have tried to report it without success.
In four recent correspondence games, I have castled only for something to go wrong. Two kings appear on the board, one on the king's original square and one on the castling destination square. These are not just graphical artifacts. I can move both kings thereafter, at least on the iPhone app.
Several times, my opponent has also told me they can see the two kings. Attempting to submit a move with the "ghost" king results in an "Illegal Move" message, but the iPhone app believes it is there. The second king does not appear on the main site and I can move as normal, but unless I have moved a piece onto the square occupied by the second king, it will appear again on the iPhone app.
While it makes it much harder to mate me with two kings on the board, I would prefer that the app be fixed! Will this happen soon?