Just a thought- maybe give the carboy a gentle swirl/shake to rouse the yeast?
From Wyeasts web site:
1338 European Ale Yeast. From Wissenschaftliche in Munich. Full-bodied complex strain finishing very malty with full bodied profile, very desirable in English Style Brown Ales and Porters. Produces a dense, rocky head during fermentation. Flocculation - high; apparent attenuation 67-71%. (62-72° F, 16-22° C)
Since the flocculation is high, maybe that would help. Are you using a carboy or a bucket? Do you see a "dense, rocky head"? It's also possible that it's about done, too, especially since you used a starter that took off.