Thanks Bob. I'm having some trouble with parts of your response as follows:
What is in your /etc/apt/preferences file?
I don't have such a file in /etc/apt
What is the relative versions shown here:
$ apt-cache policy gnucash
Because backports is set up with a repository pinning of
"NotAutomatic: yes" in the Release file it shouldn't be wanting to
upgrade your existing packages automatically. Here is a reference.
What reference?
Personally I set up /etc/apt/preferences as specified.
http://backports.debian.org/Instructions/#index3h2
I can't see any reference to preferences in this site
(sorry if I'm missing something obvious)
But if gnucash is newer than Lenny but older than backports then it
will fall into the case where it will want to upgrade to the newer
version in backports.