I have an old Stumpy with horizontal forward facing dropouts; late eighties or early nineties frame depending who is telling me, I bought the Stumpjumper book but it's not in there - thanks Specialized. Twice now, on the same short sharp climb, the rear wheel has pulled loose from the dropouts and I've had to carry the bike home because a threaded axle is more in keeping with the age of the bike than a qr. Not that I actually know the age of the bike... anyway, on inspection the dropouts don't appear damaged, and this only happens on severe climbs. Assume that I've tightened the bolts correctly - is there anything else I could do to prevent this happening?
The following photo has been scavenged from the internet, it's not my bike but demonstrates the type of dropout I mean.