pcolor in subplot

When using pcolor within a subplot, this seems to change the display of other axes in the subplot, e.g.

subplot(2,1,1)
plot(rand(20,1))
subplot(2,1,2)
pcolor(peaks), shading interp, axis off

Here, the axes in subplot(2,1,1) are not displayed. This only occurs when using pcolor - not e.g. imagesc.

Why is this? How to work around it??