Peter - are you properly booted in EFI? i.e. are you booting from a GPT disc?. It sounds to me that you are not. I had similar problems until I properly booted into EFI i.e. I could boot from a GPT disc.
I have a 4T Seagate and there are (now) no problems I can have as many partitions as I want and copy anything over. I copied over my 2T music directory without problems.
To boot into EFI a W8 install DVD MUST be in the DVD drive (W7 is no good it has to be W8). When it is go into the UEFI ("BIOS") screen and look at the devices being offered to boot from. There will now be two offered for the internal DVD rewriter - one UEFI and the other the ordinary BIOS option - select the UEFI version. I forced a boot from this by removing all other options.
So then continue out of "BIOS" to the W8 install options. You need to let W8 format the HDD - there was something wrong because I was not able to find any way to set up more than one partition at that time. However, as it turned out it was not a problem because I continued with the OS install got everything working and then afterwards used the Windows tools to reduce the OS partition size to 100Gb and create a new 2nd partition of 3.7T.
Also even though I had already formatted the HDD as GPT W8 would not install onto it until I formatted the HDD from the W8 install disc.
Before I actually got the PC properly booted in EFI I had a number of problems with the 4T Seagate that sound similar to the ones you find.