When part of a file is included via XInclude and XPointer, the recursion
detection triggers if that file contains an xi:include to a file which is
currently being processed, even if that xi:include is not within the section
being included.

For example, say we have two files, yellow.xml and orange.xml. Both contain a
<title> section, containing CDATA, and an <other_colours> section, containing
the value of the title of the other. This <other_colours> value is included by
using an xinclude with xpointer pointing at the <title> section of the other
file. libxml2 will fail to parse either of the files, because they reference one
another and this is detected as a loop, even though no loop actually exists.

Section 4.2.7 of the XInclude specification says:

  When recursively processing an xi:include element, it is a fatal error to
  process another xi:include element with an include location and xpointer
  attribute value that have already been processed in the inclusion chain.

This rule does not apply in the current case, since although the include
location is the same, the xpointer attribute value is different.