user=> (= (byte-array (map byte [1 2 3])) (byte-array (map byte [1 2 3]))) ; not equal
false
user=> {(byte-array (map byte [1 2 3])) 1, (byte-array (map byte [1 2 3])) 2, (byte-array (map byte [2 3 4])) 3} ; hashes are the same... THIS TIME
IllegalArgumentException Duplicate key: (byte-array (map byte [1 2 3]))  clojure.lang.PersistentArrayMap.createWithCheck (PersistentArrayMap.java:70)
user=> (def a (byte-array (map byte [1 2 3]))
)
#'user/a
user=> (def b (byte-array (map byte [1 2 3])))
#'user/b
user=> (= a b) ; again, not equal
false
user=> (.hashCode a) ; ...different hashes!
2137552888
user=> (.hashCode b)
545732387
user=> {a 1, b 2} ; no complaints from the hash-map constructor
{#<byte[] [B@7f6877f8> 1, #<byte[] [B@20873723> 2}

; I thought maybe the reader was caching the two arrays created in the same expression, but I can't replicate that:
user=> (map #(.hashCode %) [(byte-array (map byte [1 2 3])) (byte-array (map byte [1 2 3])) (byte-array (map byte [2 3 4]))])
(1629818866 1211763377 1519652738)
user=> [(.hashCode (byte-array (map byte [1 2 3]))) (.hashCode (byte-array (map byte [1 2 3]))) (.hashCode (byte-array (map byte [2 3 4])))]
[905154502 157559766 259650411]