ghc 7.10.3 no space leak with nested State

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.10.3

$ ghc foo.hs -fforce-recomp && ./foo +RTS -s
[1 of 1] Compiling Main             ( foo.hs, foo.o )
Linking foo ...
((),'a')
  44,000,052,712 bytes allocated in the heap
       2,717,328 bytes copied during GC
          44,312 bytes maximum residency (2 sample(s))
          21,224 bytes maximum slop
               1 MB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0     84458 colls,     0 par    0.109s   0.105s     0.0000s    0.0001s
  Gen  1         2 colls,     0 par    0.000s   0.000s     0.0001s    0.0001s

  INIT    time    0.000s  (  0.000s elapsed)
  MUT     time    9.037s  (  9.035s elapsed)
  GC      time    0.109s  (  0.105s elapsed)
  EXIT    time    0.000s  (  0.000s elapsed)
  Total   time    9.147s  (  9.141s elapsed)

  %GC     time       1.2%  (1.2% elapsed)

  Alloc rate    4,868,828,428 bytes per MUT second

  Productivity  98.8% of total user, 98.9% of total elapsed

$ ghc foo.hs -O2 -fforce-recomp && ./foo +RTS -s
[1 of 1] Compiling Main             ( foo.hs, foo.o )
Linking foo ...
((),'a')
  18,400,051,824 bytes allocated in the heap
       2,350,232 bytes copied during GC
          44,312 bytes maximum residency (2 sample(s))
          21,224 bytes maximum slop
               1 MB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0     35510 colls,     0 par    0.045s   0.043s     0.0000s    0.0001s
  Gen  1         2 colls,     0 par    0.000s   0.000s     0.0001s    0.0001s

  INIT    time    0.000s  (  0.000s elapsed)
  MUT     time    2.456s  (  2.456s elapsed)
  GC      time    0.045s  (  0.043s elapsed)
  EXIT    time    0.000s  (  0.000s elapsed)
  Total   time    2.502s  (  2.500s elapsed)

  %GC     time       1.8%  (1.7% elapsed)

  Alloc rate    7,491,409,858 bytes per MUT second

  Productivity  98.2% of total user, 98.3% of total elapsed