We had to go download the app from the App Store and were able to finally replicate the problem. It just didn't happen on our test builds on our 3G units.
As Mark correctly stated, switching to landscape (and then back to Portrait if you wish) works around the problem. Sorry for the inconvenience.
The issue seems to be related to the new iOS 5 SDK from Apple, which we started using with v4.7...
I've put together a fix which will be included in the next release, and tested it on a 3G unit, along with iPad and iPhone 4.
Since there's a fairly simple workaround, we're going to be waiting a bit for that next release in case we get any other bug reports.
Thanks for letting us know about this problem.
Regards,
Ernesto.