Может ли pugixml сама закрывать теги или игнорировать незакрытый тег?

Finally, there are two more flags, that indicate closing tag parsing. When pugixml meets a close tags, there are three ways:

check that the tag name matches the opening tag, return an error if it does not. This is a standard-compliant way, is controlled by parse_check_end_tags flag, which is on in W3C mode
try to find the corresponding tag name (so that <foo> <bar> </foo> will be parsed correctly). This is controlled by parse_match_end_tags, which is on by default
just treat the tag as a closing tag for the node (so that <foo> ... </bar> will be parsed as <foo> ... </foo>). This is the fastest way, and this is what pugxml is doing, but it can corrupt your DOM tree. This way is chosen if both parse_check_end_tags and parsse_match_end_tags are off.

http://pugixml.googlecode.com/svn-history/r2/trunk/docs/index.html

Документация из старого релиз. В новом ничего подобного найти не смог. В исходниках подобного флага нету.