When attacking parts, they appear to be placed slightly offset in the direction a kerbal is moving. it appears you are adding the part one frame after the click but relative to the kerbal, not the subject of the attachment

Initially, the part is created in the kerbal's local space, and the part is not immediately attached (it needs to get initialized). So your suggestion is correct. However, before doing the actual attach, the part is aligned against the target. I would agree there can be an edge case when this alignment doesn't work. Can you reliably reproduce this issue? Can you make a short video to demonstrate it?

This issue is likely fixed by #217. Feel free to re-open if you are able to reproduce it.

this appears to still be the case. it also might be amplified by using rescale mods, similar to the stock shrouds bug

Can you reproduce it on the launchpad using any stock part affected with a rescale mod? The compatibility issues are known to happen when another mod mangles with the part's scale. I can try to achieve a compatibility (if at all possible), but I need a simple and reliable reproducible case.

yup I'll work on some steps to accurately reproduce it. when I say rescale mod I mean rescales the solar system, not the parts