SEVERE error involving column-width property

A SEVERE error like the following appears during the PDF generation of two of the manuals:

[fop] May 8, 2007 9:48:40 AM org.apache.fop.fo.PropertyList convertAttributeToProperty
[fop] SEVERE: Ignoring property: column-width="" (file:///C:/javadb/trunk/out/adminguide/derbyadmin.fo:779:247: No conversion defined ; property:'column-width')

It appears the following number of times for each manual.

adminguide: 2
ref: 80

The messages appear to have something to do with the processing of tables, although they do not seem to have anything to do with how the colwidth attribute is specified.

The errors don't seem to affect the correctness of the generated output. For the Reference Manual in particular, however, they are a major nuisance. It would be desirable to know how to get rid of them, either by correcting the DITA source or by fixing the toolkit in some way.