Pages 4.3 on Mavericks - data loss with filenames beginning with tilde (~)
While the tilde is reserved in Unix to shortcut the users directory, it's also used by Pages, Numbers, and Keynote (as well as the Office apps) to prefix temp cache/version files.  They are invisible to the user via the Finder. I would try navigating to the folder with the command line and see if it shows up with an ls -larth.  Best advice is don't use "~" as a prefix for iWork or Office documents.