  Firstly, we prove that every closed subgroup $H$ of type-preserving
automorphisms of a locally finite thick affine building $\Delta$ of dimension
$\geq 2$ that acts strongly transitively on $\Delta$ is Moufang. If moreover
$\Delta$ is irreducible and $H$ is topologically simple, we show that $H$ is
the subgroup $\G(k)^+$ of the $k$-rational points $\G(k)$ of the isotropic
simple algebraic group $\G$ over a non-Archimedean local field $k$ associated
with $\Delta$. Secondly, we generalise the proof given in \cite{BM00b} for the
case of bi-regular trees to any locally finite thick affine building $\Delta$,
and obtain that any topologically simple, closed, strongly transitive and
type-preserving subgroup of $\Aut(\Delta)$ has the Howe--Moore property. This
proof is different than the strategy used so far in the literature and does not
relay on the polar decomposition $KA^+K$, where $K$ is a maximal compact
subgroup, and the important fact that $A^+$ is an abelian maximal
sub-semi-group.
