as discussed on http://groups.google.com/group/mongodb-user/browse_thread/thread/c5b67a50b814ce46#

When I try to update a value in an indexed list I get the error:
"can't append to array using string field name"

As soon as I remove the index, the update performs with no problems.

I have some test documents like this:

"cast" has an ascending index.

My update routine in PHP looks like this:
$collection->update(
array('cast' => 'John'),
array('$set' => array('cast.$' => 'John Travolta')),
array('multiple' => TRUE)
);

I've tried the same on the console, same result: with index I get the error,
without the index the update works.