I'm relatively new to Tinkercad an have encountered an issue. I have a stack-able box project I'm remixing from multiple sources and am trying to get the top and bottom profiles of the boxes to match. I've been trying to get the profile in the top of an object that is flush, to match the bottom by duplicating one object, aligning them on top of each other, turning the top object into a hole and grouping them. This SHOULD do exactly what I want. The issue is that when I group the object, a skin remains on the inner wall. There should not be any reason I'm aware of for the size difference with the dimensions of the box because they started as the same object. One was just duplicated and then removed as a hole. Any thoughts here? Thanks in advance.