I/O error : Is a directory - error processing a DB book withdocbook-xsl chunk stylesheet

Hi libxslt authors,

Some time ago I already reported this issue [1], but it seems I forgot
to examine it further. Today I got a private mail about the same problem
so I decided to find a testcase to debug the problem and I was able to
create a very short example, that fails for me with an I/O.

Can you please be so kind to take a look at it and verify, if it's a bug
in libxslt? In this case I would open a bug report. Please follow these
steps after saving the attached files:

mkdir built-doc
xsltproc --output ./built-doc/ book.xsl book.xml

The result for me is:

Writing ch01.html for chapter
Writing index.html for book
I/O error : Is a directory
I/O error : Is a directory

The problem seems to be related to the --output option and the doctype-*
attributes of xsl:output, because if you don't use --output option or
remove the doctype-* attributes, then the example does not fail.

I'm working with a recent Debian Sid (docbook-xsl 1.73.2, libxslt
1.1.22, libxml2 2.6.30).

CCed docbook-apps for the case, it is caused by the docbook-xsl
stylesheets and their authors can help

[1] http://www.mail-archive.com/[email protected]/msg00897.html

Regards, Daniel