Just got the new .cab from Mundu Support:
"We thank you for your feedback.
This problem with MSN seems to have recently cropped up with mundu IM.
Based on various customers feedback, our developers have worked
towards a build with fixes for the probable scenarios that might lead
to this. Attached is the same. Request you to install it on your
device, and let us know if it works for you. This build also has a
fixes for the display problems in the chat window."
http://uploaded.to/?id=o5hy5f
Now works with MSN - seemingly no issues, all other features are intact
v4.0.241 (build 11061)