At the risk of sounding pedantic: gliding IS fixed wing training. This is more than semantics, since flying sailplanes and airplanes is much more similar than, say, flying helicopters and airplanes.
I can't see how anyone would pick up bad habits from one that would compromise performance in the other. Perhaps a few minor things (e.g. most power pilots don't use their feet enough; most glider pilots have little or no radio discipline), but nothing that can't be easily overcome with a little competent instruction. On the plus side, experience in both will tend to make you a better-rounded pilot.
I agree with Mobieus1 that if your primary purpose is to build time towards a PPL or CPL, gliding experience is an inefficient way to do it. On the other hand (as he says) it's a lot of fun, and will sharpern your stick and rudder skills.
If you can find a copy in the library, take a look at Robert Buck's book, "The Art of Flying" (1984), and especially the chapter entitled "The Case for the Glider".