What would cause the engine on my outback to blow the spark plug out ofcylinder?

This plug was cross treaded at some point! See answer #1. There is no recall for improper spark plug installation!

The threads in the head are damaged and there are inserts that are designed to fix them. I'd suggest you have a pro do this but if you want to try you need to manually turn the engine over so that the exhaust valves are open on the cylinder you are working on. Connect a shop vac in leaf blower configuration to the tailpipe to push air through the cylinder and out the spark plug hole. The reason you do that is the first step of installing the insert will be to rethread the hole to a larger size to accommodate the larger insert. By using the blower, the pieces of metal removed during the rethreading will be blown out of the engine instead of falling into the cylinder. There are times that it is just too difficult to do the rethreading in the car, and your Subaru might be one of those. You may have no choice but to pull the engine and send the head to a machine shop.

check with Subaru there may be aRecall to cover this