When editing a pdf, select a value from a drop-down field. then when trying to edit a text field, the keyboard no longer appears. This issue manifests itself on iOS 6.1 and 7.0 but not on 5.1
I managed to find the issue (debugging using the libtools source code). The problems was on our code, I was using UIInterfaceOrientationPortrait instead of UIInterfaceOrientationMaskPortrait in the view controller that displayed the PDF view. The former was deprecated in iOS 6, which explains why it all worked well on iOS 5 but not 6+. This caused all sorts of problems for the keyboard without any runtime warning.