Reverting to Pages 09 format
If you even open a Pages 09 document with the icloud version of Pages, you will render it unreadable by Pages 09 (who knows why).
While it is impossible to revert directly to Pages 09 format from the icloud version of Pages, Apple support gave me a work around.
- Open the document with the icloud version of Pages;
- go to tools|download and download the document in Word format.
- You can then delete the original pages which Pages iCloud rendered unreadable and open the Word document in Page 09 and save it in Pages format.
Round about, but it worked. And it also means that you can delete the crippled, buggy Pages 5.1 from your system and forget about it unless or until Apple provides a usuable piece of software.