I never have food in the corner because of the shape, the food slides down. But, I would say that the plate would flip it you tried to cut and place pressure on the side of the plates because of the slant. You may want to go to walmart and check out the plates, they have that particular pattern and similar square plates on display. The high cost of this trendy pattern is not worth it, especially with the square plates.
yes it is unfortunately; I had to go check LOL with a flash light never noticed it was not a solid line, just specks real tightly put together to appear like lines in a charcol color. :) but I have had them for 3 years. I did have a few break on me from falling into one another, company replaced them. A few that chipped in dishwasher company gave me hassel with returning for another. But worth it in my eyes.
Enjoy them they are a beautiful set.