This (empty) instance declaration

instance Num (a,b) => Num (a,b,Int) where

produces the following error when compiled with jhc 0.8.2:

$ Temp/jhc-0.8.2/jhc Temp/jhc1.hs 

jhc Temp/jhc1.hs
jhc 0.8.2 (mydniquipepo-32)
Finding Dependencies...
Using Ho Cache: '/home/yom/.jhc/cache'

Temp/jhc1.hs:1   - Error: Invalid Class. multiparameter classes not yet supported:
(Num,[HsTyTuple [HsTyVar {hsTypeName = a},HsTyVar {hsTypeName = b}]])

Am I misunderstanding something, or is it a legitimate bug?