maybe 0008769 could be a solution

as there can be situation where I don't want to copy all attachments to a subproject by default

@ryalb
I guess you are not using the DB as storage for attachments?

This is by design. Unless we have a configurable definition of what clone means, whatever we come up with will conflict with a subset of the users.

Marking resolved - won't fix for now, as this is a current design decision