  A $k$-stack (respectively, $k$-queue) layout of a graph consists of a total
order of the vertices, and a partition of the edges into $k$ sets of
non-crossing (non-nested) edges with respect to the vertex ordering. In 1992,
Heath and Rosenberg conjectured that every planar graph admits a mixed
$1$-stack $1$-queue layout in which every edge is assigned to a stack or to a
queue that use a common vertex ordering.
  We disprove this conjecture by providing a planar graph that does not have
such a mixed layout. In addition, we study mixed layouts of graph subdivisions,
and show that every planar graph has a mixed subdivision with one division
vertex per edge.
