Callback fires on graph creation even with prevent_initial_call=True

We have a callback with the following inputs

Input({'type': 'heatmap-delta', 'index': MATCH}, 'relayoutData'),
Input({'type': 'heatmap', 'index': MATCH}, 'relayoutData')

callback also has prevent_initial_call=True

but when graphs with this patterned Id are created we always see the callback fire. callback_context.triggered is, e.g.

[{'prop_id': '{"index":1,"type":"heatmap"}.relayoutData', 'value': {'autosize': True}}, {'prop_id': '{"index":1,"type":"heatmap-delta"}.relayoutData', 'value': {'autosize': True}}]

Isn’t this exactly what prevent_initial_call=True should be preventing from happening in this case?