Default Help ! All Files not getting moved/copied from phone to PC in MTP

I own a MOTO G & have been facing this weird issue while copying/moving files from my phone to PC.

After selecting all the files in the phone explorer (mtp mode) & trying to copy them to my win8.1 notebook, the process automatically terminates/window vanishes midway. There's no error/warning thrown but all files do not get copied. I have tried to do the same thing many times but failed everytime. I tried to copy 6GB of files/folders. Everytime only 4GB gets copied & remaining (some folders with data) left out. why is this happening ? is this because they are being copied in mtp mode ?