It changed in Products.PloneHotfix20160830 version 1.3 -- see Security patch has been released: 20160830 - #7 by mauritsvanrees
There is now an attribute allow_prefill_from_GET_request which can be set to True to still allow this (default: False). easyform does this explicitly: collective.easyform/view.py at master · collective/collective.easyform · GitHub