When you did the "hold on", you implicitly froze the log vs normal scale of the plot axes, so the loglog() will be treated the same as the plot().
Any one axes only has a single XScale and a single XScale. It is not possible for a single axes to display a plot in normal scale and log scale at the same time. You can use plotyy or the newer yyaxis calls to create two axes, one for each of the scales.
But you need to avoid using "hold on" before loglog() -- that or else you need to
set(gca, 'XScale', 'log', 'YScale', 'log')
which is what loglog() mostly does internally.
