Hm, this is getting hard to answer. Adding normal instances of ZCLasses to other ZClasses should work. Are you adding everything straight from the management interface or programmatically from DTML? If from the management interface, are you sure you always add TinyTable etc from within the instance? If programmatically, could you send the code?
Perhaps you could try and adding one of the problem products in another way (from a dtml method instead of the management interface or the other way around).
The items I'm adding aren't other ZClasses, but rather from python products. I haven't come up with an exhaustive list of which items cause the problem and which don't, but I know at least the TinyTable and ZMySQL DB Connection do, and the DTML Methods/Documents, MailHost and UserFolders don't.
Everything is being added via the interface. I haven't tried adding them via DTML. I've never done that because I haven't had a use for it, so I'm not sure I know how.
I setup a series of screen shots to demonstrate exactly what's happening. Take a look at http://www.logicetc.com/Test/zclass_problem if you're interested.
I looked at it, and found it fishy. The strange thing is, I tried to reproduce it, but I can't. To be sure I added a tiny table plus to an instance not a straight tiny table and a ZODBC adapter, but I doubt whether this would make a difference. Anyway, they both work straight away. This is getting very strange indeed. It seems strange things are happening to your namespace. I can think of some things that may cause problems, but this is all speculation. This may be a bug, but then it's a special one. Anything special about your ZClass - what does it derive from (just objectmanager? anything else that might cause strange behaviour?). Is there a subobjects tab in it's definition? Are the products in there? Rik