Mischievous

Turning on my local public radio station this morning to listen to Car Talk, I instead heard one of those insidious pledge breaks that I am so tired of. The droning voice, referring to the Car Guys, said he liked the mischievious way they answered questions.

According to the Merriam-Webster's 11th Collegiate Dictionary (online version), that spelling and pronunciation, while they are common and go back to the 16th century, are non-standard.

It's mischievous, not mischievious.