JDK 7's sort function is stricter about verifying that implementations of the comparison function actually obey their contract. It will even helpfully throw an exception when this is not the case:

java.lang.IllegalArgumentException: Comparison method violates its general contract!

The root cause is this gem:

(defn shuffle
      "Shuffle coll"
      [coll]
      (sort-by (fn [_] (long)) coll))

Which does not work on JDK7 since TimSort is clever enough to detect that the ordering function is behaving inconsistently, resulting in the previously mentioned exception.

Also, this is just a bad idea:

A variant of the above method that has seen some use in languages that support sorting with user-specified comparison functions is to shuffle a list by sorting it with a comparison function that returns random values. However, this is an extremely bad method: it is very likely to produce highly non-uniform distributions, which in addition depends heavily on the sorting algorithm used.

(wikipedia)

ASCII 127 is a control character.

Dec Hex    Dec Hex    Dec Hex  Dec Hex  Dec Hex  Dec Hex   Dec Hex   Dec Hex  
  0 00 NUL  16 10 DLE  
  1 01 SOH  17 11 DC1  
  2 02 STX  18 12 DC2  
  3 03 ETX  19 13 DC3  
  4 04 EOT  20 14 DC4  
  5 05 ENQ  21 15 NAK  
  6 06 ACK  22 16 SYN  
  7 07 BEL  23 17 ETB  
  8 08 BS   24 18 CAN  
  9 09 HT   25 19 EM   
 10 0A LF   26 1A SUB  
 11 0B VT   27 1B ESC  
 12 0C FF   28 1C FS   
 13 0D CR   29 1D GS   
 14 0E SO   30 1E RS   
 15 0F SI   31 1F US                                                 127 7F DEL