Something I've finally figured out the source of...
When editing a document with a linked image on a computer that does not have the linked image causes the document to be truncated. The image apears as a red outline in the document, but when the document is saved, the rtf is cut off. Adding the linked image to the local computer seems to fix the problem reliably. This was not a problem in v4 as sometimes we intentionally did not distribute the linked images.
for example:
{\headerf{\tblstart1{\trowd\trleft0\trftsWidth3\trwWidth10766\clftsWidth3\clwWidth4258\clvertalt\cel
lx4258\clftsWidth3\clwWidth6508\clvertalt\cellx10766\pard\intbl\itap1\li0\fi0\ri0\sb0\sa0\ql\plain\f
1\fs24\b{\*\wptools\wpomode0\wpoframe0{\*\wppicname{C:\\\\ProgramData\\\\image.jpg}}{\*\wppicsource{C:\\ProgramData\\
image.jpg}}{\bin292
at the end, there are a couple ASCII characters like blocks. Any ideas on what I can check if this might be something I'm doing? The images are inserted using the standard WPT image dlg.