I Keep getting a weird duplication happening with my units, its hard to pin point when, but in this scenario, it is a 80% custom unit. It happened when i had closed part editor, used the prompts page to then adjust the height of the unit to make sure the parts followed correctly. at that point it duplicated. One is almost dead to the system, it doesn't duplicate and show 2 of the products in the lists, its still one, unit, functions as one unit, and can use prompts as one unit. But the old original version (not the duplicated one) has the spec of the new version of the height, but is not drawn like it. The original i will delete and proceed to carry on with the duplicated version. Hope that makes sense!

1 extra thing, it duplicates in place of the original, so the first screenshot is what happens, 2nd screen shot is me moving them apart. 

Can also tell the original is a 'dead' unit by when highlighting it, it selects parts, not the whole unit like default.  screenshot 3.