Y limits affect axis position?

This has been driving me crazy. Generate two axes with the same y positioning, one half the width.

a1=axes;
a2=axes;
a1pos = get(a1,'Position');
set(a2,'Position',[a1pos(1)+a1pos(3)/2,a1pos(2),a1pos(3)/2,a1pos(4)]);

Now change the limits of one of them:

ylim(a1,[2.555 4.0]);

The two axes have the exact same y-positioning, but the plots are slightly offset relative to each other in the y direction! I confirmed that all the position properties are still the same, so what's going on?

Answer 1

[Mischa Kim]

Kurt, this should work:

 ylim(a1,[2.555+eps 4.0]);

[Kurt]

I figured out that small changes in the limits can change this behavior, but what's actually going on? Why would an infinitesimal change in the limits do this? I don't want to have to keep screwing around with them to fix this in the future.