The eraser tool leaves the layer after being used.

[kijaecheong]

After I draw something at the layer, and use the eraser tool, it leaves the color of the layer that I used the brush tool on. It is seen when I turn on paint on transparent.

It isn't seen when paint on transparent is turned off.

For instance, I draw something on a picture of someone's face, and use the eraser tool to get rid of my mistake, I can see the layer where the brush has been. 

Here is the screenshot of the part that I am struggling on.

[Rick Gerard]

When you have paint on transparent selected you must have a target layer selected. If you want to remove brush strokes select the layer with the brush strokes, press UU to show all modified properties, and turn off or delete the brush strokes you want to remove. The eraser tool actually adds another stroke. 

Paint is a bit confusing and the online documentation is not very good, but the info is in there if you look hard enough.

One more thing, please embed your screenshots so we can see them. Uploaded screenshots are a real pain to look at and the Toolbar makes embedding just as easy as uploading. Cropped screenshots are also useless for diagnosing problems. Select the problem layer, press 'uu' then take a screenshot of the entire UI so we can see what you are doing to the layer.