aZaZel writes:

... "uniqueValuesFor" not updated after modification ... Almost surely a small bug in ZCatalog.

A field index is implemented as a mapping from values to lists of documents. "uniqueValuesFor" returns this mapping's "keys()". When the field value of a document changes, this document is removed from the corresponding list. Obviously, a test is missing whether the result is the empty list. If it is, the key should be deleted. Probably, you can fix this yourself. The code is in "SearchIndex.UnIndex". If you fixed it, file a bug with patch report into the Collector. Dieter