GHC panic durring MVar operation

The following error message was displayed while loading a program into ghci by executing :r in a ghci session:

ghc.exe: panic! (the 'impossible' happened)
  (GHC version 7.8.3 for x86_64-unknown-mingw32):
        thread blocked indefinitely in an MVar operation

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

The only edit made to the source file before compiling was the removal of an unnecessary do on line 20 of the source file. The do was used even though the monodic computations were written in a single line style.

I have not been able to reproduce the panic at all. The source file, unedited since the panic, now compiles without error.

The ghci session leading up to the crash is below

*Main> :t runState (filterM untouchable [1..3]) M.empty
runState (filterM untouchable [1..3]) M.empty :: ([Int], M.Map Int Int)
*Main> runState (filterM untouchable [1..3]) M.empty
([2],fromList [(1,1),(2,1),(3,1),(4,3)])
*Main> runState (filterM untouchable [1..10]) M.empty
([2,5],fromList [(1,1),(2,1),(3,1),(4,3),(5,1),(6,6),(7,1),(8,7),(9,4),(10,8),(11,1),(12,16),(13,1),(14,10),(15,9),(16,15),(17,1),(18,21),(19,1),(20,22),(21,11),(22,14),(23,1),(24,36),(25,6),(26,16),(27,13),(28,28),(29,1),(30,42),(31,1),(32,31),(33,15),(34,20),(35,13),(36,55),(37,1),(38,22),(39,17),(40,50),(41,1),(42,54),(43,1),(44,40),(45,33),(46,26),(47,1),(48,76),(49,8),(50,43),(51,21),(52,46),(53,1),(54,66),(55,17),(56,64),(57,23),(58,32),(59,1),(60,108),(61,1),(62,34),(63,41),(64,63),(65,19),(66,78),(67,1),(68,58),(69,27),(70,74),(71,1)(72,123),(73,1),(74,40),(75,49),(76,64),(77,19),(78,90),(79,1),(80,106),(81,40)])
*Main> runState (filterM untouchable [1..100]) M.empty
([2,5,52,88Interrupted.
*Main> *Main>
*Main>
*Main>
*Main>
*Main>
*Main>
*Main>
*Main> :r
[1 of 1] Compiling Main             ( C:\Users\admin\Programming\Haskell\codegolf\Untouchable.hs, interpreted )
Ok, modules loaded: Main.
*Main>
ghc.exe: panic! (the 'impossible' happened)
  (GHC version 7.8.3 for x86_64-unknown-mingw32):
        thread blocked indefinitely in an MVar operation

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Related
Blocking
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