xcopy bug with mounted directory?

[di]

xcopy j:\pictures w:\backup\pictures /M /E /V /C /I /F /H /R /K /O /X
/Y

j:\pictures contains several folders, one of them is a mount point to
another volume, called Pictures2.

That directory does not get copied with the following message:

File creation error - The directory is not empty.
Unable to create directory - W:\backup\pictures\Pictures2

this is not a permission issue etc. I experience this behaviour only
with mounted volumes and xcopy.

Thanks for help.

D.