What counts as 'dronepart stacking'?

[JMPowell86]

I just fired up the game after some time away to find almost 100% of my designs are now unusable due to a 'dronepart stacking' restriction added in the last patch.  I've experimented a bit with removing and rearranging parts, but haven't been able to determine exactly what counts as a stacked part.  On several designs, I found that removing one nacelle or the other removes the restriction, while I would have expected that it would be necessary to remove both if a conflict existed with either.  Other designs were acceptable after the removal of seemingly random components.  I love the game, but I'm a bit frustrated by the opacity of this new restriction and would certainly appreciate a little guidance on how to avoid it.  Thanks in advance for any help!

[Waity5]

I think it is any drone part which is ontop of another drone part

 

[JMPowell86]

While that's certainly what the name implies, in-editor testing suggests something else is at play.  The restriction is quite possibly bugged, but I thought it might be worthwhile to see if anyone else had a similar experience with old designs being disqualified for no discernible reason or any insight into the issue.