Let $G$ be a finite group with proper non-trivial subgroups $H$ and $K$.
If $H K = K H$, then $H K$ is obviously a subgroup of $G$. It is well-known that $H$ or $K$ being normal implies that $H K$ is such a subgroup.
Question: Is there a finite group $G$ with proper non-trivial subgroups $H$ and $K$ such that $H K = K H$ and neither $H$ nor $K$ is normal in $G$?
Example In $D_4$ $H=<s>$,$K=<r^2s> $ Clearly HK is subgroup of G But None of H and K is normal subgroup.