[xml] 2.6.26 xpath returns too many nodes?

[Arnold Hendriks <a hendriks b-lex nl>]

We recently upgraded from libxml2 version 2.6.13 to 2.6.26, and are now 
running into problems with the xpath code. It appears that, very 
infrequently, the result of xmlXPathEvalExpression contains too many 
nodes (the correct node and a handful of nodes that appear a bit later 
in the document, but not necessary only the immediate siblings or chilrden).

The problem is hard to reproduce, and would appear to be some sort of 
race condition. So far I can't come up with a testcase that consistently 
reproduces it. The 2.6.24 libxml2 however, works fine.

This is a win32 build, using C++ Builder 5, and I'm checking 
xmlHasFeature(XML_WITH_THREAD) at startup to make sure I've really got a 
threaded version of libxml2. The code is running inside a multithreaded 
webserver using a thread pool, but in this specific case, the xmlDoc and 
xpath expressions aren't accessed by different threads (the code fails 
during the 'startup' phase of a http request handling, and the objects 
are not passed between threads in that phase yet)

Any suggestions on where to look for the problem?

Thanks in advance,
Arnold Hendriks