This was previously thought to be an isolated issue, but appears to be widespread. For example, when hitting /api/v2/users you can see the 'last_login_on' field is showing too much information:

{
"total": 1,
"subtotal": 1,
"page": 1,
"per_page": 20,
"search": null,
"sort": {
"by": null,
"order": null
},
"results": [ {
"id": 3,
"login": "admin",
"firstname": "Admin",
"lastname": "User",
"mail": "root@example.com",
"admin": true,
"auth_source_id": 1,
"auth_source_name": "Internal",
"last_login_on": {
"time": "2014-10-13T14:39:06Z",
"time_zone": {
"name": "UTC",
"utc_offset": null,
"tzinfo": {
"identifier": "Etc/UTC",
"real_timezone": {
"info": {
"identifier": "Etc/UTC",
"offsets": {
"o0": {
"utc_offset": 0,
"std_offset": 0,
"abbreviation": "UTC",
"utc_total_offset": 0
}
},
"transitions": [],
"previous_offset": {
"utc_offset": 0,
"std_offset": 0,
"abbreviation": "UTC",
"utc_total_offset": 0
},
"transitions_index": null
}
}
},
"current_period": null
},

oj 2.10.4 is believed to fix the problem. Please run "bundle update oj" if you run into it.