  We analyse backward Euler time stepping schemes for the primal DPG
formulation of a class of parabolic problems. Optimal error estimates are shown
in the natural norm and in the $L^2$ norm of the field variable. For the heat
equation the solution of our primal DPG formulation equals the solution of a
standard Galerkin scheme and, thus, optimal error bounds are found in the
literature. In the presence of advection and reaction terms, however, the
latter identity is not valid anymore and the analysis of optimal error bounds
requires to resort to elliptic projection operators. It is essential that these
operators be projections with respect to the spatial part of the PDE, as in
standard Galerkin schemes, and not with respect to the full PDE at a time step,
as done previously.
