Description:
------------
The value of a $_POST array item is not being assigned properly

Test script:
---------------
<form method="post">
<input type="submit" name="step4[edit][change]" value="Submit and continue">
<input type="submit" name="step4[edit]" value="Continue without changes">
</form>

<?
//After form submission
var_dump($_POST['step4']['edit']['change']);
?>

Expected result:
----------------
//When "Continue without changes" is pressed, expected value:
NULL

Actual result:
--------------
//When "Continue without changes" is pressed...

//Actual value:
string(1) "C"

//The "C" is taken from the first character of the value of $_POST['step4']
['edit']

//A var_dump of $_POST['step4']['edit'] returns the value as expected as does a 
var_dump of $_POST['step4']['edit']['change'] when that is actually pressed.