Highlights and shadows brush turns into hand after zooming

I'm noticing some strange behavior from the Highlights and Shadows brushes. I don't remember seeing this before though.

I have one H & S overall adjustment to lift the shadows ab bit.

Now I add a second one and set it to reduce the highlights but with the "Brush adjustment In" option. I adjust the brush size and I start to paint over the hot areas of the image. But nothing seem to change.

Then I zoom in a bit and now the brush turns into a hand. Even when I go back to the brick and reset it to "Brush Adjustment" the cursor only funstions as a hand.

Only if I go back to default size does the brush re-appear.

Then if I uncheck this second adjustment brick to see a before and after and then turn it back on, now the adjustment goes over the whole image instaed of just the areas that I painted.

Any idea of what might be happening here?

I am using v 3.4.5 on OS 10.8.5.

Thank you

Bo.