The moderation API works just fine for submitted objects.
The code, admin/moderation.php, however makes a difference for users and the rest.

Within the custom_member registration I've coded a transaction to submit some comment to the moderator(s). This shows up in the moderation menu. After 'processing' by the moderator(s) the comments are deleted.
Now, this transaction just uses a field within the custom_memberinfo table. No separate submissiontable. In order to have this work for me, I've change admin/moderation.php: added the test

just before the place where item is deleted from the submissiontable
and where the submissiontable is copied into the table.
I think the test is harmless and adds safety. Maybe this should make it into CVS?

Of course, I feel good with this. It opens up the possibility when using the API to work with transactions or have your code tested without loosing all the testdata. Just by nullifying the submissiontable.

FYI: when a user fills in the 'purpose' field of his membership, merely to communicate a request or question, the field shows up in the moderation menu. The moderator follows up the request and deletes the purpose field. See this as a replacement for an email, since the email address of the moderator(s) is not known at all times.