Using a custom tile size that isn't cleanly
divisible by your pattern grid means pattern tiles
will have anti-aliased (blurry) edges. (It won't
have any effect on shape tiles.)
If you're after pixel-perfection, use one of the
preset sizes (8, 16, 32, 64, 128, 256) which work
nicely with the pattern grid sizes (8, 16, 32).
Custom Grid Size
Warning: Anti-aliasing Ahead
Using a custom grid size that doesn't divide evenly
into your tile size will create anti-aliased
(blurry) edges when the pattern is exported.
If you're after pixel-perfection, use the preset
options for both tile and grid sizes.