php strpos offset outputs different
<p><strong>What</strong> is it that causes this <strong>difference</strong>?</p>

<pre><code>echo strpos('abcdef abcdef', 'a', 0); //output= 0
echo strpos('abcdef abcdef', 'a', 1); //output= 7
echo strpos('a b- c a b* c a b+ c', 'c', 0); //output= 5 
echo strpos('a b- c a b* c a b+ c', 'c', 1); //output= 5 (But why? Is is must be 12)
echo strpos('a b- c a b* c a b+ c', 'c', 6); //output= 12
</code></pre>