Incorrect function signature causes the impossible to happen

I made a mistake in my function signature:

> cat wibble.hs 
ecase :: Either a b -> (a -> c) (b -> c) -> c
ecase (Left a) f _ = f a
ecase (Right b) _ g = g b

> ghci wibble.hs 
GHCi, version 8.2.0.20170507: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/erikd/.ghci
[1 of 1] Compiling Main             ( wibble.hs, interpreted )
ghc: panic! (the 'impossible' happened)
 (GHC version 8.2.0.20170507 for x86_64-unknown-linux): repSplitAppTys
 a_a1pA[sk:1]
 c_a1pC[sk:1]
 []
 Call stack:
  CallStack (from HasCallStack):
   prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1134:58 in 
         ghc:Outputable
   callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in 
         ghc:Outputable
   pprPanic, called at compiler/types/Type.hs:808:9 in ghc:Type

GHC 8.02 correctly reports an error:

GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/erikd/.ghci
[1 of 1] Compiling Main             ( wibble.hs, interpreted )

wibble.hs:1:24: error:
    • Expecting one fewer argument to ‘a -> c’
      Expected kind ‘* -> *’, but ‘a -> c’ has kind ‘*’
    • In the type signature:
        ecase :: Either a b -> (a -> c) (b -> c) -> c

Trac metadata

Trac field	Value
Version	8.2.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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