SUMMARY The "Pixel Art Fill" base brush isn't symmetrical. STEPS TO REPRODUCE 1. Select "Pixel Art Fill" brush. 2. Use 6px size as an example, but the bug exists with various sizes. 3. You can use various ratio setting (eg. 0.50), it makes it even less symmetrical. 4. Click somewhere in the canvas. EXPECTED RESULT You get an unsymmetrical circle. ADDITIONAL INFORMATIONS Maybe the internal brush have an offset. I'm really not an expert, sorry but I can't help more.
*** This bug has been marked as a duplicate of bug 359858 ***