I have created a ceiling with a hatch pattern. I have done this before and it worked without a thought. It has a MODEL hatch pattern: this has never been an issue before, the line drawing renders fine in 3d view. Now, if I use a MODEL hatch pattern, it ends up in plan and elevation as skewed.
Same thing, changing only the pattern to a DRAFTING hatch pattern, and the 3d view of the ceiling looks fine. The ceiling family's lines are all at 90d to each other, no skewing. The slope is 6:12.