Copying MPEG to new HDD: LENGTH attrib becomes "unspecified"

....in the RHS of the navigation pane (Windows 7 / Windows Explorer)

LENGTH is still an attribute of the copied file because DETAIL PANE (at bottom) shows the expected LENGTH value (hh:mm:ss).

Could this be related to getting rid of thumbs.db on the 2nd drive (HGST 4TB)? I had thought that 7 did not use Thumbs.db anymore but I have had mixed results in eradicating ihis everywhere on my system.

A 3rd HDD (Seagate 4TB) does not have this problem (Identical BACKUP of the BACKUP).

BTW: Seagate 4TB is NTFS and HGST 4TB is GPT (FWIW)

Surely this is something stupid I have overlooked (or screwed up!)

TIA
---JCN9801

Somehow I had the top level MPEG folder set to READ ONLY (did not seem to inhibit copying new files though). Once I reset this property (and to all sub-folders) all of the MPEG file LENGTH attributes appeared in the RHS of the Navigation pane as expected. Go figure!

My bad?

---JCN9801