Copying many files with Windows Explorer halts prematurely

I have a Dell Studio laptop that comes with Windows 7 Home Premium 64-
bit. It looks perfect except one thing:

Once I copied the ~/.purple directory (which stores user data for
Pidgin, an instant messenger from http://www.pidgin.im) from a Linux
machine to a USB hard disk, and then from that USB hard disk to the
Windows 7 laptop.

That .purple directory mostly contains a lot (tens of thousands) of
chat log files (plain text files). When I copied this directory from
the USB hard disk to Windows 7 using Windows 7's Windows Explorer, the
Copying File dialog box automatically disappeared when the copying
progress was in the middle. (About half of the files were not copied.)

Then I used XCOPY to copy the directory, and it was successful.

So, the problem seems to be that Windows 7's Windows Explorer failed
to copy many files at a time. Maybe it's because the Clipboard that
held the filenames to be copied is too small to hold tens of thousands
of filenames. Or maybe Windows 7 doesn't recognize some Linux
filenames.