var_dump() should not touch the cursors in arrays, it should work with a copy of this arrays, it should not manipulate them directly, performance is not needed using var_dump() - I think.
One has to reset() every array after using var_dump(), it this is expected behaviour, it should be documented.

Expected result: ab[dumped stuff]c
Current result: ab[dumped stuff]

<?php
$t=array('a','b','c','d');
print reset($t);
print next($t);
var_dump($t);
print next($t);
?>