11.2.0.1 11GR2 connect_by_use_union all fails.

Hello,

I am dealing with a known issue of 11.2.0.1 SW. We have upgraded our Oracle SW from 11.1.0.7 to 11.2.0.1 and we have come against the known issue of bug 9920616 (connect_by_use_union_all fails).
I am overcoming this issue by running the commd below:

alter system set "_connect_by_use_unionall" = old_plan_mode SCOPE  memory;

However this is not a permanent solution since whenever the instance is restarted the setting is reset.

Could you guide me of how to overcome this issue by a permanent fix? May I set it somehow in init file? Just to let you know that our instance is getting started by pfile so is there any way to set the old plan mode in pfile?