Create a new group (pre-made groups don't work for this). When making a group enable "receive pms" checkbox.
The group should have no members.
Now go to ucp and compose a pm. Select this new group as the recipient. Press send. Recipient/group will be accepted.
Press send again. The following message is shown:
No recipient defined.
This is wrong as clearly I have defined a recipient and the software even accepted it.
The actual problem, which is that a group with no members was selected, should be communicated more clearly.
Is this message only possible when pming groups? If so perhaps acceptable language would be "The selected recipient groups have no members", possibly after checking that all recipients are groups.