Ever since upgrading my father's installation of WordPress from 2.6.2 to 2.6.3 he is no longer able to past from word without getting the <!-- [EndIf] --> issue.
A lot of people are experiencing the same thing and are generally getting the response "don't paste from word"
This is all very helpful for the future but does not tackle the real issue that this used to work prior to 2.6.2 and no longer works from 2.6.3 upwards. TinyMCE has a facility to automatically cleanup word code so I am wondering whether TinyMCE was upgraded or the configuration changed with this release.
I am raising this an issue on Trac as although it is easy to blame MS I believe in this instance there is an issue either with WordPress or TinyMCE.
Others who are experiencing the issue: