SOME .docx files open in compatibility mode

[Bruce]

Can anyone point me to where I can determine what elements may be
causing some DOCX files to open in compatibility mode in word 2007 and
word 2010 Beta? What seems strange is that if I open the document,
make a change to it and resave it, when re-opened, it will STILL be in
compatibility mode. However, if I open the document, do NOT change
anything, and then re-save it under a new name and re-open it, then it
does NOT open in compatibility mode. All functions and features I use
seem to work fine either way including embedded XL spreadsheets.

OS: win7Pro32 1.5 GB RAM All files saved to local drive in all
instances; single user system; no domain.
Word 2007 and Word 2010 Beta NOT on the same system at the same time.
I believe all the docs exhibiting the problem were created originally
in Word 2007.

 

[Bruce]

An interesting update:

I just noted that if I create a new document via File > New > Blank
document > Create the new doc comes up with the header bar title
of New Document [#] (Compatibility Mode) so it is in
compatibility mode even before keystroke one and is not an issue with
imported settings from an old file because the system was wiped when I
went to Win 7 / Office 2010.