[oli merge]

Actually, after thinking about it, Doug's answer does solve the problem as I
effectively have to make the same amount of queries for each mail merge
template anyway using the aforementioned dodgy Word recipients query options.

I think having access queries may actually be the way to go after all, I
will probably substiture the mail merge queries for access queries as I
encounter problems.

Since it doesnt look like anyone can give a reason for the original problem
of the criteria changing itself I will mark this question as answered (due to
Doug's work around). However, if anyone does know how or why this is
happening it would be good to make a MS knowledgebase article about it.
Thanks.