I can't reproduce this:

<?php
$xml = <<<'EOX'
<?xml version="1.0"?>
<parent>
    <child attr="foo">text content</child>
</parent>
EOX;

$doc = simplexml_load_string($xml);
printf("Text content: %s; attribute: %s\n", $doc->child, $doc->child['attr']);
?>

Outputs "Text content: text content; attribute: foo", as I'd expect. Are you 
able to provide a reproduction script?

The SO discussion appears to be about JSON encoding only; given that 
SimpleXMLElement doesn't support serialisation, I'd suggest that the same would 
apply to JSON encoding.

another test:

$xml = <<<'EOX'
<?xml version="1.0"?>
<data>
<datum file-key="8708124062829849862">corn</datum>
</data>
EOX;

$doc = simplexml_load_string($xml);

echo $doc->asXML();

echo print_r($doc);

This is not a problem with loading for me - I am building my SimpleXML object 
dynamically.
The output from asXML() is correct.
The output from print_r() is not.
The output using attributes() (in a more complex example) is not correct, 
although this simple test does work.

I am experiencing this on various versions of PHP 5.3.X on Windows Vista and 
Ubuntu 11.10.

(ubuntu)$ php -v
PHP 5.3.2-1ubuntu4.9 with Suhosin-Patch (cli) (built: May  3 2011 00:45:52)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
    with Suhosin v0.9.29, Copyright (c) 2007, by SektionEins GmbH

(Windows)>php -v
PHP 5.3.8 (cli) (built: Sep 22 2011 20:51:51)
Copyright (c) 1997-2011 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies

Ah, I see what you're getting at now. Thanks. It appears to be an issue with the 
get_properties and get_debug_info handlers for SimpleXMLElement.

This has been reported and closed as a duplicate before, but I think that was 
mistaken, as we don't have an open bug for this at present that I can find.

I am having exactly the same problem and it is not feasible to add an extra tag to all of my "text" entries.

Is there any update on this one? A 3rd party PHP library I'm using has a defect 
which, I think, is caused by this problem because the phenomenon is that attribute 
in the XML node is not loaded, and that XML node happens to have text content.

Just by way of a note, this problem is still occurring in PHP 5.5.24.

> This has been reported and closed as a duplicate before, but I
> think that was mistaken, as we don't have an open bug for this
> at present that I can find.

There is bug #44973, which has been closed as not a bug.

To clarify: not only attributes may be swallowed in debug output,
but also elements of mixed content.

The bad "fix" has been reverted – re-opnening.