Let K be a field and g(K) a Chevalley group (scheme) over K. Let (B,N) be the
standard spherical BN-pair in g(K), with T=B\cap N and Weyl group W=N/T. We
prove that there exist non-trivial elements w\in W such that all
representatives of w in N have finite order. This allows us to exhibit examples
of subgroups of g(Q_p) that act Weyl transitively but not strongly transitively
on the affine building Delta associated with g(Q_p). Such examples were
previously known only in the case when g(Q_p)=SL_2(Q_p) and Delta is a tree.