Additive merge for dict with list values?

[oerp-odoo]

I have these dictionaries as a sample:

Y1 = {'migration': {'options': {'install_command': 'odoo2'},
  'versions': [{'version': 'setup',
    'operations': {'pre': ["echo 'pre-operation'"]},
    'addons': {'install': ['crm'], 'upgrade': ['note']}},
   {'version': '0.1.0',
    'operations': {'post': ["echo 'post-operation'"]},
    'addons': {'install': ['web', 'contacts']}}]}}
Y2 = {'migration': {'options': {'install_command': 'odoo'},
  'versions': [{'version': 'setup',
    'operations': {'pre': ["echo 'pre-operation-2'", "echo 'pre-operation'"]},
    'addons': {'install': ['account', 'crm'], 'upgrade': ['note', 'hr']}},
   {'version': '0.1.0',
    'operations': {'post': ["echo 'post-operation'",
      "echo 'post-operation-2'"]},
    'addons': {'install': ['purchase', 'sale']}}]}}
Y3 = {'migration': {'versions': [{'version': '0.2.0',
    'addons': {'install': ['mrp', 'stock']}}]}}

I merge it like this:

from mergedeep import merge, Strategy

d = merge({}, Y1, Y2, Y2, strategy=Strategy.ADDITIVE)
print(d)

And get this output:

{'migration': {'options': {'install_command': 'odoo'}, 'versions': [{'version': 'setup', 'operations': {'pre': ["echo 'pre-operation'"]}, 'addons': {'install': ['crm'], 'upgrade': ['note']}}, {'version': '0.1.0', 'operations': {'post': ["echo 'post-operation'"]}, 'addons': {'install': ['web', 'contacts']}}, {'version': 'setup', 'operations': {'pre': ["echo 'pre-operation-2'", "echo 'pre-operation'"]}, 'addons': {'install': ['account', 'crm'], 'upgrade': ['note', 'hr']}}, {'version': '0.1.0', 'operations': {'post': ["echo 'post-operation'", "echo 'post-operation-2'"]}, 'addons': {'install': ['purchase', 'sale']}}, {'version': 'setup', 'operations': {'pre': ["echo 'pre-operation-2'", "echo 'pre-operation'"]}, 'addons': {'install': ['account', 'crm'], 'upgrade': ['note', 'hr']}}, {'version': '0.1.0', 'operations': {'post': ["echo 'post-operation'", "echo 'post-operation-2'"]}, 'addons': {'install': ['purchase', 'sale']}}]}}

Yet I expect lists to be appended. For example from dicts Y1, Y2, install key in setup version, is ['crm'] and ['account', 'crm'], yet first one is kept values from Y2 is ignored. I expect it to become ['crm, 'account', 'crm']

Is my assumption is incorrect and mergedeep works as intended?