If php-file with unknown extension starts with "<?php" ("" just for clarity), it is not regocnized as php-file.
If it starts with "<?php ", then it is regocnized as php-file.

Is there really a need for the space character?

See screen captures of test file, one with space and another without space in
https://onedrive.live.com/redir?resid=FCCA3C47C268C13A%217100