class EmailFilter is causing issues

Hi, i already posted issue that this plugin shows error that

The e-mail could not be sent.
Possible reason: your host may have disabled the mail() function..

To solve this issue i installed wpMandrill, with wpMandrill it is sending emails but are empty(i.e. email body is empty)…and sometimes there is 0 in message body instead of original message.
But after spending a lot of time, I figured out that in forgot_passsword.php file this line of code

$message = $pie_register_base->filterEmail($message_temp,$user->user_login, '',$key );

is causing this issue. when i modified this line of code to

$message = $message_temp;

It is working now.. but variables in message body like

%user_login%, %reset_password_url%, etc.

are not replaced by their corresponding values

https://wordpress.org/plugins/pie-register/