Unmodified iOS7 Apple GLPaint example blending issue

Question

In Apple's GLPaint example, the user can draw with semi-transparent brush over a surface and change colours.

However, as of iOS7, for some odd reason it is not possible to draw something that completely goes over its background: In the first image, we see "Shake me" written with green and a red blob that was drawn multiple times over it. Yet, the writing bellow is still barely visible. The second image was desaturated to make the defect more obvious.

The OpenGL blending function Apple is using is:

glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

What I expect it to do is to blend the newer semi-transparent brush strokes over their background until it cannot longer be seen.

How do I modify the example to achieve such traditional blending?