I'm sorry, but I still cannot reproduce this bug. Sometimes updating to the latest TB version helps. Currently it is Thunderbird 16.
Also you may enable debugging option and look at TB error console. If the MNP doesn't stop generating traces after you use arrows then there is indeed something wrong with MNP. If it stops generating traces then there is something wrong with your system
I've fixed several unrelated bugs. You may find update here:
http://forum.alehro00.com/Bug-on-version-1-4-0-4-tp4637619.html