Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves. 

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external 
resources such as databases, etc. If the script requires a 
database to demonstrate the issue, please make sure it creates 
all necessary tables, stored procedures etc.

Please avoid embedding huge scripts into the report.

<?php
	function parse( $xml ){
    
		//$this->_parserMemory = array();
		$parser = xml_parser_create('UTF-8');
		
		xml_set_object($parser, $this);
		xml_parser_set_option($parser, XML_OPTION_SKIP_WHITE, 1);
		xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, 0);
		xml_parser_set_option($parser, XML_OPTION_TARGET_ENCODING, 'UTF-
8');		
		xml_set_element_handler($parser, "_xmlTagOpen", "_xmlTagClose");
		xml_set_character_data_handler($parser, "_xmlCdata");
		
		if (!xml_parse($parser, $xml)) {
			$this->_children = array();
			$error_code = xml_get_error_code($parser);
			$error_string = xml_error_string($error_code);
			$current_line = xml_get_current_line_number($parser);
			$current_column = 
xml_get_current_column_number($parser);
			
			echo ("Parser error #{$error_code}: {$error_string} on 
line {$current_line}, column {$current_column}.");
		}
		
		//unset($this->_parserMemory);
		xml_parser_free($parser);
     }
     
    $xml = '<simplexml>
				<name>PageControl</name>
				<title>Paginabeheer</title>
				<version>1.0.0</version>
					<cms_routes>
						<index type="default" 
inMenu="true" authlevel="50">
							<title>Overzicht</title>
								<parts>
								
<part>pagecontrol</part>
								<part>*</part>
                            </title>
                         </index>
                    </cms>
                </version>
          	</simplexml>';
    parse( $xml );
         
?>

https://bugs.php.net/bug.php?id=55353
SIMPLEXML []
    NAME []
        #text: PageControl
    /NAME
    TITLE []
        #text: Paginabeheer
    /TITLE
    VERSION []
        #text: 1.0.0
    /VERSION
    CMS_ROUTES []
        INDEX {"TYPE":"default","INMENU":"true","AUTHLEVEL":"50"}
            TITLE []
                #text: Overzicht
            /TITLE
            PARTS []
                PART []
                    #text: pagecontrol
                /PART
                PART []
                    #text: *
                /PART
XML Parser error 'Mismatched tag' in (data stream):311(13,37)
Stack trace:
#0 …/XmlParser.php(106): org\rootdir\Wrapper\XmlParser->parse('<simplexml>\n\t\t\t...', true)
#1 …/xml-test.php(200): org\rootdir\Wrapper\XmlParser->parseString('<simplexml>\n\t\t\t...')
#2 {main}

Which is 100% expected considering the open tag is "<parts>" but closing one is "</title>". And there's one more mismatch too: "<cms_routes>"/"</cms>", also "</version>" closed twice.

After fixing the three mentioned issues with provided sample, it parses perfectly.

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

Indeed, invalid XML is not necessarily supported by the XML Parser.