If you follow the bug report page, there are two interesting patches that fix completely the problem.
While it is true that it is not a roundcube problem because its the mailserver that sends the wrong bodystructure, it is also true that its roundcube goal to show me my emails and it does me no good at all when roundcube fails at that.
Said this, the patches in the bug report do work perfectly and do address the problem fully: when the bodystructure is broken, just show the raw email data so that me, as an end user, can still see the email, which is why i use roundcube.
The rest is only mental games: roundcube is used to show email, so it have to show emails even if the server response are not 100% standard. Otherwise, people simply stop using it because it fails on the most basic and most important task: to show emails.
So please do not ignore all this but include in trunk the second patch in the bug report.
By the way, there is no blame here. Nobody blames RC or HM (hotmail), we just want to be able to read our email. Then, if horde works i use horde and stop using RC. But i like RC more and i believe in making it a better product so this is why i am here. Now what should i do? Go to all my hotmail friends and tell them to switch email? Go to hotmail iteself and say hey guys, you have to upgrade all your servers because what since all other mail clients out there works?
If you follow this line of tought we would not have a single line of deployed AJAX in the world because IE has never been fixed properly.