Mask prepend string performance

[Sydnic]

Hi, There was another post about this, a while back, but there was no suggestion to a workaround. The problem is when I have a known string as part of the passphrase, i am including it in the mask like this: "pass?l?l?l?l". This however reduces my performance by a lot! From 11000 MH/s to 250 MH/s. If I were to append it after..like "?l?l?l?lpass" , this wouldn't reduce the performance at all. Is there a way to avoid this? And why does this happen..is it a bug?