12-03-2017, 05:47 PM
Normally it should have been disabled because you were using "Fill whole selection", right? Otherwise, that may explain it, because one important thing to know is that the Magic-Wand selection and the Bucket-Fill tool (but only in "Fill similar colors" mode) have one thing in common: it's either all or nothing. They cannot do partial work on pixels, a pixel is either fully painted/selected or left alone depending on which side of the threshold it is. The consequence is that these two tools will mercilessly destroy anti-aliasing. This is a very common pitfall for beginners, dug and enlarged by countless ill-advised tutorials.