I think never.
It may contain multiple vouts, but each should have only one address. Even with multisig, I think the address shown would be the hash of the multisig script.
Then it's funny that the field is called "addresses" instead of "address" and that it's actually an array, instead of a plain scalar:
"vout" : [
{
"value" : 0.01055000,
"n" : 0,
"scriptPubKey" : {
[some stuff],
"addresses" : [
"17BXw4qwrKv8bd8gLZtYj75V368K88GJW6"
]
}
},
vs (hypothetical):
"vout" : [
{
"value" : 0.01055000,
"n" : 0,
"scriptPubKey" : {
[some stuff],
"address" : "17BXw4qwrKv8bd8gLZtYj75V368K88GJW6"
}
},
There must be some reason to this.