Why does Windows append .php to my php files but not other ones

Solution 1:

Two things are most likely on your system for this to happen:

1. The option Hide extensions for known file types is checked.

2. You haven't registered the PHP filetype to your system and thus is an unrecognised file format.

These combined will show .php file extensions while other documents are hidden.

You can change this when you open a folder and go to: Tools > Options > View

There you'll see the option to uncheck Hide extensions for known file types. Do so and save.

If you want to hide the PHP file extensions, leave the extensions option hidden and just register the filetype.

Solution 2:

Look at one of the PHP file properties from explorer.
Maybe its called filename.php.php !!

You seem to have your filename extensions visibility set to hidden.
But, that does not work when you have the extension two times.