Grouped Flat View and Uncompressed archive size column

I see some strange behavior with Uncompressed column when viewing a flat grouped display:

Fig.1 As you see if an item already exists in the root with the same name - only then is the uncompressed file size calculated for the nested item.
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Fig.2 Strangely enough, adding another archive (with different size but the same name as the one not being calculated) to the root folder suddenly makes the nested one be calculated and both sizes are correct.
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Fig.3 Renaming the same file in the root and refreshing - nested another_archive loses its uncompressed size
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Fig.4 Having no files with the same names in the root folder = no calculation whatsoever
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Version: DOpus 12.7.3 x64