Apologies if this has already been logged, I searched and couldn't find a prior reference.
As the pictures show, I mount drives not on drive letters but on directories (Unix style). MC appears to be a bit confused and leaves the tree view name of the directory blank. Also, strangely enough one directory (Flash Drives) is being shown with the top level tree names (A:, C:) in place of the blanked dir names. I use this directory as the link point for all my thumb drives media card reader mounts.