Thanks Fiona - actually I have been finding that that happens with the iPad (which I also use) across many forms (not just within Moodle). Indeed it is a known issue but the work around is to close the keyboard and open the keyboard on the iPad and the cursor will be back.
Apologies that it isn't ideal. We have it on a "wish list" to get something better in place but since it is across forms on many environments, not just Moodle, I feel I have to go with "it is an iPad, not Moodle" answer.
Hope this is useful. And happy iPadding with Moodle.
Fiona