Old migration to rename packing to shipment is causing problem in upgrade

I have defined a new model "shipment_packing_station" in my module. This module depends on stock. While upgrading register fails with following trace:

File "/Users/prakashpandey/.virtualenvs/tryton/lib/python2.7/site-packages/trytond/pool.py", line 155, in init
lang=lang)
File "/Users/prakashpandey/.virtualenvs/tryton/lib/python2.7/site-packages/trytond/modules/__init__.py", line 429, in load_modules
_load_modules()
File "/Users/prakashpandey/.virtualenvs/tryton/lib/python2.7/site-packages/trytond/modules/__init__.py", line 398, in _load_modules
load_module_graph(graph, pool, update, lang)
File "/Users/prakashpandey/.virtualenvs/tryton/lib/python2.7/site-packages/trytond/modules/__init__.py", line 237, in load_module_graph
cls.__register__(module)
File "/Users/prakashpandey/.virtualenvs/tryton/lib/python2.7/site-packages/trytond/modules/stock/shipment.py", line 194, in __register__
& (model.module == module_name)))
psycopg2.IntegrityError: duplicate key value violates unique constraint "ir_model_model_uniq"
DETAIL: Key (model)=(shipment_station) already exists.

I figured out the old migration is causing problem. How long do you support the migrations? 1.2 is very old now I guess? Let me, happy to send a patch.