I have the same issue described here for the iWorks suite with two further apps, "PDF Expert" and "GoodReader". And the common point is, that I access a document in the iCloud, access it then from another device (iPad), make possibly a little change (such as adding a bookmark to the PDF file I was reading), reading it then again on the iPhone, and if I stay in the document, if I do not leave the document inside these apps, then, and apparently only then, but surely then, the iPhone resets whenever I click on the home button, either once to go to the home screen, or twice, to go to another app straight away. It may happen a second or a few seconds after having left the culprit, but it will happen. In the Diagostics informations in the Settings app I will find the same reason for a Kernel Panic Reset than for the iWorks resets, it is always happening on a daemon process called "backboardd".