Corner Board/Quoin

[05uurx]

Anybody have any ideas about this? I've drawn others like this with brick on one wall and siding around the corner and this didnt happen.

-1" thickness on Quoin

-i double checked to make sure that the wall material and Quoin material were the same brick texture/pattern

-i tried making the Quoin thicker, but still the same

-the other corners work fine under same circumstances