This may have been covered already but in case not:
I was having trouble with a 60x60 pixel png button placed 5 pixels in and up from the bottom right of the iPhone screen. Basically it wasn't responding to touch. As a test, moved it in to the bottom centre of the screen and it seems to work fine.
I figure this must be something to do with the "tap&slide" action of showing the black screen to show the errors/KRPano version, there effectively seems to be a 'blind spot' for placing touch-sensitive plugins down in that bottom right corner. There is an equivalent plugin bottom left of the screen and this works fine.
Also, if I make the plugin bigger but keep it anchored in the same x/y position, it responds when you touch the top left of it, but not in the middle of the plugin image. Again, this suggests to me a 'blind spot' at the bottom right.
Malcolm