GW8 (Not HP1).

User creates a message to send to recipient(s).
Adds 3 attachments to message (Any kind or combination that can be opened.
DOC, PDF, TXT ...)

The first selected attachment can be opened by double clicking.
Each subsequent attachment can not be opened for editing, but only for
viewing, regardless of host editor.

This behavior has been observed on 2 independent systems.
In GW7 each attachment could be opened for editing by double-clicking on the