REST call for process startform returns ISO-8859-1 charset

Call to new REST endpoint **/flowable-rest/service/repository/process-definitions/MY-PROCDEF-ID/start-form** always receives response with "Content-Type: application/json;charset=**ISO-8859-1**", while other requests seems to receive "application/json;charset=**UTF-8**" (which is desireable).

P.S. Same thing happens with task form request (/flowable-rest/service/runtime/tasks/MY-TASK-ID/form).