QUOTE
I said it was a bug for XTRA. Base mode is supposed to have the addons attach.
Actually, it's not a bug.

Xtra places by the pixel so that the placement ends up being most likely offset. If you placed it with perfect orientation, I'm sure addon would attactch.
QUOTE
scmdraft 2 properly attaches the addons when they have correct orientation, I suggest using the building snap for this (so snap to tile)
Thank you for your lovely bit of SCMDraft advertising