[Zope] symbols undefined after product refresh?

[Jürgen Herrmann]

hi!

after reloading my own products through the zmi it seems like some
classes and methods gets undefined. please see the following
traceback:

...
  Module Python expression
"here.zuml_parseAndCheckinModel(newConfigDict)", line 1, in <expression>
  Module Products.IDE.IDEContainer, line 176, in zuml_parseAndCheckinModel
  Module Products.Relateable.MetaManager, line 474, in recreateIndexes
  Module None, line 104, in addSubClassCatalogMethod
TypeError: 'NoneType' object is not callable

the code @ line 104 is:
    o = SubClassCatalog(id, searchKeys, subClassNames)

SubClassCatalog is defined in /Products/SubClassCatalog/SubClassCatalog.py,
after I refresh the Product "SubCLassCatalog", i get the error mentioned
above. restarting Zope fixes the Problem, MetaManager::recreatedIndexes()
will work repeatedly until i refresh one or more Products...

did i miss something while importing stuff?
/Products/relateable/MetaManager.py imports the constructor for a
SubClassCatalog like this:
from Products.SubClassCatalog.SubClassCatalog import addSubClassCatalogMethod

i'm pretty puzzled at this point, hope someone got a hint...

regards, juergen herrmann

ps: this does not only happen to my SubClassCatalog, this also hits
f.ex. "from random import randint" where randint gets undefined.