AstraSync uses the SmartReply in the ActiveSync protocol when sending forwarded messages to reduce the amount of traffic. This is why the original message and attachments to forwards should be added by your server.
As this is not happening then their would appear to be an issue with the OpenXchange server when utilizing the SmartReply protocol rather than an issue within AstraSync itself. Whether this is a setup issue with OpenXchange or a server bug we don't know so you would need to ask OpenXchange for help relating to this.
Vicky Cwilewicz
AstraSync Support
www.astrasync.com