So there is nothing interesting in kernel log on both sides whe copying data? Still if you are using the device as card reader, I'd try to remove card an use card reader or clone over ssh without using tablet's usb storage.

A for the usb disconnect - if you don't have MENU_X_USBMODE set for that item in bootmenu.conf I don't know how it can be different from internal flash. You may also try to enable framebuffer console and watch the screen. For that you need additional modules in initfs. Search this forum for bitblit fbcon softcursor or see http://wiki.maemo.org/Advanced_booting