Hello Jules,
it seems that arrows in CallOutBoxes are very rarely drawn in iOS, as you can also verify by running the Juce Demo. The OS X version instead works as expected.
I'm using the Xcode 5.0.2 iOS simulator. Am I missing something?
It's probably just because there's not enough space - the arrows aren't drawn if the calloutbox overlaps the thing it's trying to point to.
Did you try the Juce Demo on an iPad? I do not think this is the case.
I did try it, and AFAICT it works as it should do. There was a recent discussion about this: http://www.juce.com/forum/topic/calloutbox-question