Ive found an inconsistency in the returned form of isrcs when using JSON search API.
I am only finding the isrcs in the for of a kvp when "Search" requests return, as in contrast to Browse/Lookup requests where only an array of isrc values are returned.

So for example when requesting:
http://musicbrainz.org/ws/2/recording/?query="Blow%20Your%20Mind"&fmt=json

In each returned recording you will find each isrc in the kvp form:
"isrcs":[

{"id":"GBAMC9900024"}

,

{"id":"GBAMC9900025"}

]

but as mentioned all other Browse/Loolup request return something like:
"isrcs":["GB01A0801425","GBCHB9810013"]

and from what im told this is inconsistent with the what the xml API defines.
(I havent used the xml API) thus im assuming its a bug rather than an improvement