We recently "updated" a number of document templates that we use with Word
2007. These templates have extensions of .dot.

Following the changes users suddenly found they couldn't open any of the
DOCX files created with from the earlier DOT files. They kept getting a
message of the form "Template A4_Letterhead.dot is locked for editing". In
some cases, Word simply crashed when you tried to open the docx files.

I replaced the updated dot files with the originals (I'd backed them up just
in case) and now everyone's files open fine.

My question is, what is it about the new docx format that seems to link it
to the original template file from which it was created? If such a linking
does occur, is there a way to turn it off?