ICloud – Do Pages, Numbers and Keynote for Mac/iOS offer real-time collaboration on shared documents like Pages, Numbers and Keynote for iCloud do

You can share a pages document from your iPhone. Instead of clicking "Edit", then the share icon, try clicking the document itself, and opening it. Once you have opened the document on your iPhone, click the spanner icon in the top right. A list of options will appear. Click the one that says "Share and Print". Now click "Email Document". You will be given an opportunity to choose whether to email a Pages, PDF, or Word document. After selecting the appropriate option, an email window will appear, with the document as an attachment.

I eventually worked around this by turning of iCloud in both accounts, clearing the iCloud directories and then turning everything back on. Still no idea why it was happening in the first place.