I've tested with 0.5 and 0.6 and got the same problem..
The message I receive from roundcube+flash comes just like daniel.torido described, with the weird 3D characteres. If I create a new message with my mail client by just copying the code from the message and removing the weird characters highlighted by daniel.torido, and send the message, it comes right, with the flash animation in it!
Any ideas folks??