Multiply defined error for instances of types imported qualifiedly

It seems to be impossible to instantiate a class for two types that are imported qualifiedly. The following causes a "multiply defined" error on the current stable/itask compiler:

module inst

class c a :: a

instance c 'inst_a'.A where c = 'inst_a'.A
instance c 'inst_a'.B where c = 'inst_a'.B

definition module inst_a

:: A = A
:: B = B