I mentioned to Rich Nickoley that most rigid wings I know of are more 'pitch active' in turbulence because of their pitch stability. Rigid wings have a fairly linear pitch moment versus angle of attack in the range before stall. Gliders that are more pitch stable will 'follow the air' more closely in gust conditions. Imagine moving a weather vane through a thermal at 30-mph speed. These are transient effects but are very noticeable to us pilots.
Rigid wings behave more like the weather vane than flex wings.
It may feel uncomfortable but it is perfectly normal and possibly safer because the wing that pitches is less likely to have a gust induced stall. Of course flex wings have their own tricks for avoiding stalls such as gust-load induced twist, but that's another story. The idea of a wing pitching down and accelerating into an up-gust is equivalent to what happens on a bird's wing on the down stroke of the flapping cycle. The opposite happens when hitting sink. Gary Osoba has been investigating taking advantage of this effect for more efficient soaring.