informaltable must not occur in the descendants of table

hi,
I have a docbook 5 file with a captioned html table that contains
'tr/td/para/informaltable'.

I can see in the docbook 5 reference that the combination is illegal,
but I thought that in the more recent 5.1b2 specs, it was legal.
http://www.docbook.org/tdg5/en/html/html.table.html

Of course, when opening the document with XMLMind 4.9.1 I get the
validation error:
"informaltable must not occur in the descendants of table"

However, when I use xerces, oNVDL.jar and the docbook 5.1b2 nvdl
specification, the document validates.
Also, xmllint validates the file using docbook 5.1b2 relaxng.

My question is whether I really should not have the nested table, or
should I not trust the nvdl/relaxng validation ?

thanks,
--Tim Arnold