InstanceSigs suggestion not accepted

Attached testcase compiles, but when uncommenting either of the lines 19, 21 or 23, I get an error:

pr7908.hs:23:12:
    Method signature does not match class; it should be
      (>>-) :: forall (c :: k -> *) d.
               Hidden k c -> (forall (a :: k). c a -> d) -> d
    In the instance declaration for `Monad' k (Hidden k)'
Failed, modules loaded: none.

But in fact I basically copied the suggestion into my file! (with slight modification "Hidden k c" --> "Hidden c")

This may be because of the rank2 type or because of the polykinds appearing.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

\"Hidden c\")\r\n\r\nThis may be because of the rank2 type or because of the polykinds appearing.","type_of_failure":"OtherFailure","blocking":[]} -->