To reproduce the bug, unpack the following file and run make.
http://hyperkrychle.cz/etc/libxsltbug.tar.gz
The result is in example.txt.

The template "ctor-args" is called 3 times exactly the same way, but for the
first time it gives different (incorrect) result. This is because of a weird
behavior of the choose/when part of the "class-lookup" template. Note that the
strange behavior disappears if you replace the 'choose/when' by a single 'if'
statement, which should be exactly equivalent.

I have discovered that the 'href' attribute is (for the first call) not
accesible from inside the 'when' element, but there is an attribute 'name'. Try
to uncomment the second 'value-of'. This shows that libxslt changes the actual
node after evaluating the condition. It is somehow switched to the node found in
the test.

And furthermore I found out that it has something to do with keys. If you remove
the <key/> element from the stylesheet, it behaves correctly. And if you change
the match attribute of the key, it behaves badly but the @name is suddenly not
accessible from the <when/> element. The <key/> definition affect the strange
context switching, although it's never used.

MSxml and 4xslt behave well at this point.