Mystery duplicate co-domain appearing

[bolero]

I have one web where suddenly the exact same hostname appears twice in the co-domain listing. I can't delete it. When I try to do this I get a message about missing permissions. I think this is actually just a generic message for something that wasn't expected to happen. I checked the ispconfig database for any obvious hints, but this domain appears only once in the isp_isp_domain table. At the moment there's only one other domain in the table that belongs to a second web. The main difference I can see between the two is that the problem domain has an empty host value while the other domain has NULL as a value.
I tried to understand how ispconfig determines which domain belongs to which web and which web to which customer etc., in the hope I could then find the bogus entry that has to be there, somewhere. Am I correct in assuming that this is all defined in isp_nodes?
Any hints what creates this bogus co-domain entry?

Addition: the appearance of this bogus domain is consistent with the summary that lists 5 domains. Two webs, each with one www host and one without host = 4 domains. Plus this bogus domain (which is also without host).

[falko]

Am I correct in assuming that this is all defined in isp_nodes?
You should check isp_isp_domains, isp_nodes, and isp_dep.

[bolero]

I got rid of the problem before I read your reply. I checked isp_nodes, found an orphaned domain entry for this web and removed it. This did not fix it. But then deleting the domain the usual way moved both domains to the trash and emptying got rid of both of them. I did not look in isp_dep at that time. Or, actually, I looked, but couldn#t make sense of it.
I now had a look at isp_dep again, in case I may still need to fix something or just remove a non-referenced orphan. But that table is much more of a mystery than isp_nodes. I see that there are six records with child_doctype_id of 1015 (=domain), but I have only four co-domains. If the six should include the two main web domains (4+2), then the records are all correct. Otherwise there are probably two too much?
Is there some documentation about the tables and their dependencies?

[till]

in isp_dep are the dependencies for several records for a website, e.g. co-domains, users, databases.