I got google here for the same symmetries.
In my case, it was just Windows Explorer, which hid file extensions.
A good trap for casual Windows users like me.
So instead of having a file called index.php, I had index.php.txt.
I installed the extension using this procedure: http://kb.winzip.com/kb/entry/26/
The key was: I did not have an IDE icon in my php file.
I don’t know if my answer really helps, 5 years after the initial question ...
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