Depends on a few factors. Valves don't move or wiggle on their own, so step one is to see what's going on. Be sure to mount tires with the valve straight, and keep them fully inflated so the tire doesn't creep. If you notice your valves are crooked after a while remount.

The greatest stress on a valve happens during pumping with a hand held thumblock pump. It's easy to stress or wiggle the valve with every stroke, and this is the single biggest cause of valve breakage. When pumping grip the pump in a "hitch hiker's" grip with your thumb braced against the rim or tire, and your index finger around the end of the pump. This will keep the pump stead with respect to the valve and rim.

Also, do not pump a tire with the wheel braced because, if the pump slips or shifts in your grip the entire pumping force will go against the valve. Instead pull the wheel away from what it's leaning and let the bike rock with your pumping action.

Lastly, not to let Trek off the hook, there is a problem, but it's not just them. In an effort to cut costs, some tube makers are using valves where the brass tube is shorter than before, and now no longer goes all the way to the tube. Instead it ends outside the rim, with an un-reinforced rubber tube below. This is perfectly made so that it's very easy to snap the valve off at the rim.

Trek doesn't make the tubes, but they pick their suppliers, and are only too happy to use the lowest bidder and save one cent per bike and let their customer live with the problem.

These "short valve" tubes are also sold in the after market, so when you buy a tube, open the box and feel whether the brass valve stem continues all the way to the bottom, or comes up short.