"Apparently circular structure being printed"

[Sam Steingold]

GNU Emacs 24.0.50.4 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1)
 of 2010-11-07 on sysu76
 '--with-x-toolkit=gtk'

In an nXML buffer:
C-h v rng-compile-table RET

I get an error in the *Messages* buffer:

Entering debugger...
debugger-setup-buffer: Apparently circular structure being printed

no *Backtrace* buffer is created.
my print-circle is t.

-- 
Sam Steingold (http://sds.podval.org/) on Ubuntu 10.04 (lucid)
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