I think the behavior is right.
Did you hope for a different result?
Thank you for answer.
Can I ask more?
Why 2 flat options have same results whether GOLDEN appears or not?
If I want to get different result as hier option, what can I add to ruledeck?
GOLDEN is a very hierarchical focused statement. It is used in conjunction with several other statements that can recognize cells even if you don't know the name ahead of time (when they match a cell in the golden file).
The flat behavior reports the duplicate cell probably because the same cell name exists in both files (and the flat run may ignore the GOLDEN keyword while the file is still allowed to be used as another LAYOUT PATH filename. Multiple LAYOUT PATH filenames are allowed for both flat and hier runs.
For the hierarchical run, the GOLDEN keyword apparently signals to hierarchical Calibre to avoid reading the file in with the other files (avoid merging together that is) but instead keep it off to the side just for checking for existence of cells that match other cells in the other files when the GOLDEN keyword is used for other statements or cell operations.
If you could rename the cells in the GOLDEN library so that they would not conflict with any cells in the regular design database then they might not conflict (or attempt to be merged) with the regular cells in the flat run, but may still be available for special use in a hierarchical run?
I haven't worked with these capabilities myself so I'm speculating for most of this but I hope it helps. Based on my other experience with Calibre it makes sense to me it could work this way.