It seems that this sometimes happens when you pick up parameters from one covering to another. It does not seem to be consistent so a little hard to trace but I have had this happen too. Just adjust the corners as shown by s2art and you should be OK.
I have had some complex wall conditions where it is not possible to get the result I want but not too often.
Cheers,
Gerald
"The simplification of anything is always sensational" GKC
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