Equipment used in this problem: iPad Air, Apple wireless keyboard (MC184J/B), Apple Pages app (2.2.1).
This problem occurs when you are using an external keyboard like Apple’s wireless keyboard on an iPad to input Japanese text into Apple’s Pages.
When zoomed at greater than the width of the entire page text alternatives for your input is off the left side of your page as in the image below. This makes it difficult to select which input alternative you want.
To work around this bring up the virtual keyboard. The alternatives are then displayed at the top of this. You lose a lot of screen space but at least it works.
Not sure why Apple has not noticed this problem before or even fixed it (where do customers go to make complaints and suggestions?).