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.

Here is the problem with XPath:
<?php
$xml = <<<XML
<?xml version='1.0'?>
<document>
   <test>foo</test>
   <test>bar</test>
   <test>baz</test>
</document>
XML;

$sXML = simplexml_load_string($xml);
$arr = $sXML->xpath('/document/test');
foreach ($sXML->xpath('/document/test') as $element)
	unset($element);

echo $sXML->asXML();
?>

Expected is that there are no <test> nodes, actual is that the 
document is unchanged. Yet, in the foreach loop if I add 
$element['attr'] = 'Attribute'; (so replacing the unset line) the 
document is modified (all of the <test> nodes have <test 
attr="Attribute">...</test>).

So I can modify xpath results yet I can not unset them, The same 
applies to foreach ($sXML->test as $element), one can change but not 
unset.

can you provide an example where removing using offsets doesn't work 
(i.e. unset($xml->test[0]);)? The other things you mentioned are 
expected behavior.

Calling unset in your prev example just unsets the variable. You must 
call unset on a member of an SimpleXMLElement in order to remove it 
(i.e. unset($sXML->test[1]);)

> can you provide an example where removing using offsets doesn't work 
(i.e. unset($xml->test[0]);)?

I have just tried to replicate this, but alas, cannot. Sorry about that.

> Calling unset in your prev example just unsets the variable.

That functionality makes it very hard to unset the results of an xpath 
query. This is because one just has an array of nodes, making unsetting 
them extremely difficult.

For functionality like that you would need to import the nodes from the 
xpath output into DOM and use its capabilities to get the parent and 
then remove the child.