You seem to be re-inventing the wheel by using text boxes. Word provides the
envelope address & envelope return paragraph styles for placing addressee
and return address, so it might help if you used those. There is a size #10
envelope template you can use as a basis for creating a merge envelope
document for download from my web site. See also
http://www.gmayor.com/changing_envelope_layout.htm and
http://www.gmayor.com/Alternative_Return_Addresses.htm
It is difficult to imagine what the problem might be (a language issue?),
but adding a \*charformat switch to the fields (or replacing any
\*mergeformat switches with \*charformat switches) might help. See
http://www.gmayor.com/formatting_word_fields.htm

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Graham Mayor - Word MVP
My web site www.gmayor.com
Word MVP web site http://word.mvps.org
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> Word 2003 mail merge envelope #10:
> Layout: Two text boxes - Sender Address details etc (top left of env)
[quoted text clipped - 8 lines]
> per session but reverts on next open.
> No probs with any other docs. Does not occur in Word 2002.