I am trying to teach myself more of how photoshop works as I run a local camera club and am wanting to teach them how to remove objects using the background eraser tool. I have created a layer mask below the main image and filled it with yellow. I then go back to the main image and try the Background eraser tool having selected the background colour (in the case an obviouse Pink) set at Discontiguous (same happens with contiguous) and 50 % Tolerance (have also tried smaller). Problem is (as you will see by my image) it also paints over the non matching colours in the image and cant find where I am going wrong.
Have you found out any more about his problem? I stumbled on to it and it's really ticking me off. I was working as expected for a day or two. No updates or installs of any kind but it just stopped working properly, same as you are having. I'd appreciate any info.