Are you sure they tilted? It's more possible they swiveled slightly. The catch for the swivel sits in a hole that is maybe 1/16" wider than it each side. We have noticed that the seat can move slightly (swivel) side to side as you corner. Not so disconcerting when you know what is causing the issue.
To be clear, this happens only occasionally, and is not a large movement. Overall we like the CTA swivel (the brand name of the one sold by Swivels-r-us).
Our experience with S-R-U was that they did not communicate at all, and in combination with their archaic e-commerce system that left us with very little confidence in them. The swivels did arrive in one piece, but with the wrong nuts (1.25 pitch rather than 1.5 pitch). That shows a dangerous lack of attention to detail somewhere along the line.