I've got the latest version of update-manager now, and the problem has gone.
Before upgrading update-manager though I checked the versions of what synaptic thought it had installed, and what update-manager wanted to install. update-manager wanted to install evolution 2.10.2-1 synaptic thought it had installed 2.6.3-6etch1 At time of writing 2.10.2-1 is "testing", and 2.6.3-6etch1 is "stable". synaptic wasn't upgrading because my Distribution preferences in synaptic said "Always Prefer" "stable", hence synaptic didn't want to upgrade evolution. Which is still slightly curious - though appears fixed in update-manager 0.68.debian-1 I have now gone with testing (my preferred choice anyway). Many Thanks Chris Goldsmith
