t7861 gives unexpected result (deferred type error)

I'm not sure why validate does not trip on this, but the test case does not look obviously disabled to me, so I thought I'd just report it so at least it doesn't get unnoticed.

GHC 7.8:

"Hello"
t7861: t7861.hs:11:5:
    Couldn't match type ‘a’ with ‘[a]’
      ‘a’ is a rigid type variable bound by
          the type signature for f :: A a -> a at t7861.hs:10:6
    Expected type: A a -> a
      Actual type: A a -> [a]
    Relevant bindings include f :: A a -> a (bound at t7861.hs:11:1)
    In the expression: doA
    In an equation for ‘f’: f = doA
(deferred type error)

On GHC 7.10 the result is (both with and without optimization)

"Hello"
"Bad"

Trac metadata

Trac field	Value
Version	7.10.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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