YouTrack Rest API 5.1.1 Json response changed

It appears that a breaking change has been introduced in the current version of  the YouTrack API, whereas a result of 'sub' items previously was formatted like:

"assigneesLogin": {
    "sub": [
            {"value": "username"},
            {"value": "username2"}
        ]
    }

it now is listed like:

"assigneesLogin": [
    {"value": "username"},
    {"value": "username2"}
  ]

The Xml result appears to keep the old structure.

It would have been nice if this was to be announced (and the upgrade of , or even better and more restfull, if the url were to contain a version number.

This change doesn't seem to be mentioned in the release notes:
http://youtrack.jetbrains.com/releaseNotes/JT?q=version%3A+5.1.1+%23Fixed+%23Verified&token=c2jv8hajstlfhfka1g33knx2&showDescription=false&showComments=false

And the documentation shows only the Xml response (which is still correct), for instance:
http://confluence.jetbrains.com/display/YTD5/Get+Accessible+Projects

This is the second time in a row that the response has a breaking changed without warning, which is becoming quite a nuisance.
Is there a way I could have prevented this?