PHPStorm file type association and instance problem Follow

Hello,

I  want to associate php files with amazing phpstorm but when I do so and  double click a php file or select Open With from context menu, each file  is opened in a new instance of the phpstorm which is bad in terms of  memory consumption and not the ideal thing. When you double click an  associated file, it should open it currently open instance of the  phpstorm rather than creating yet another instance of it.

Is this an issue with phpStorm or am I missing something?

Please suggest a solution to this issue. Thanks