It all started when I got the STi - hard braking would set off the seat belt tensioners.
Then I did a Stage II upgrade, and hard acceleration would set off the seat belt tensioners, too. It got even worse when I had it pro-tuned.
Now I've finally put the upgraded sway bars on the car, and after some extensive 'test-driving' last night (very scientific, of course), I've found that hard cornering sets off the tensioners now.
...Don't you just hate it when everything your car can do sets off the seat belt tensioners?

Whee....