Saving Master document saves weird random sub documents

Hiya,
I am using Vista/Word 2007, and I am creating a master document,
inserting sub documents, then clicking Save.

Word first saves the master document, then it starts a process of
saving one file for each sub document with filenames like
"DB5A8891.docx".

So if my master document contains 3 sub documents Word first saves the
master doc, then tries to save 3 documents with these random looking
file names (all different and similar to the one above).

Weird thing is, if thats not weird enough, some of these docs save,
and some fail to, just sits there saying "Word is saving
DB5A8891.docx" in the status bar, till I stop it. And after this
first save subsequent saves dont cause this behaviour.

However if I add more sub documents, Word again tries to save these
random files, one for each new subdocument.

The master and the subdocs all reside in on my normal personal network
share at work, for which I obviously have full control, and the weird
random docs attempt to save on the root of this drive.

Any help appreciated.