Continuing from a previous thread re the new matshow(), adding a colorbar() causes the matrix to shrink relative to the colorbar. Furthermore this colorbar overlaps with the figure title.
For those like me who need a colorbar as a legend and/or who do not want the matrix visualisation in a new figure with aspect ratio constrained, all that needs to be done is to replace line 1424 in pylab.py for matshow() as follows
# OLD LINE: fig = figure(fignum, figsize=figaspect(A))
fig = gcf()
You're probably best off to create a new function matshowB() in case you ever need the default functionality.