Slow copy with mapped drive not with UNC path

Slow copy when:

Open explorer window to a mapped drive and move a file from the mapped drive to a second explorer window to the same mapped drive.

Fast copy when:

Using only one explorer window

or

Using two explorer windows with a UNC path in lieu of the mapped drive.

Thoughts?

I tried both scenarios but I can't get the same effect. Both transfers where normally fast!!

Any way this might help: support.microsoft.com/kb/885189