I get the message "Cannot retrieve raw message" when I try to view a raw event. Same problem for both FWSM and IPS.
Most annoying since the enhanced functionality of this feature was one of the main reasons to upgrade from 4.3.6 in the first place. What I can find in the backend log is "RawmsgBufferReader: read end of the buffer, not find two separators". That doesn't tell me anything more than that it might be a bug.