Word 2003 Compatibility Mode in Word 2007 - Problem Saving..

This problem involves documents saved under Word 97/2000/2003 in word
document format but WITHOUT THE .doc EXTENSION TO THE FILENAME on a network
path e.g. \\File-Server\Link$\directory\1\123456789 (where 123456789 is the
filename of the Word document). When the file is retrieved in Word 2007 the
(Compatibility Mode) heading is shown as you would expect; but, changes to
the document when clicking the Save button or using the Alt-S shortcut are
not saved and no error is presented. If the document is on the local machine
or has a .doc extension the changes will be saved. True on original load of
Word 2007 as well as SP1.