Still Fementing after 17 days

[RishoBrew]

Brewed a partial mash Toad Spit Stout from Joy Of Home Brewing. Had the OG of 1.070 so "stepped" up my yeast using a stir plate method. After 17 days it still bubbling (constant frothy bubbles) in the primary. I never had my batch fermenting this long, although this was the first time using a stir plate and a step up method. Has anyone had a similar experience?

 

[JLeuck64]

Yup! I've had bigger brews like that show sign of activity in the airlock for a month before! ( ;