when you do 'make menuconfig' you get the option to enable write support for the ntfs filesystem. since the gentoo-sources have the new ntfs driver patched in this becomes untrue. there is no write code in the new ntfs driver at all. so you cant compile with write support enabled. if you try to write to a mounted ntfs partition you will get a permission denied.
hmm... well it says it is experimental and dangerous, so I kinda wonder why you were trying it... anywho, I'll try to add a little patch to make the option go away.
this is up to the originators of the ntfs-linux patch... unless you feel the desperate urge to send me a patch to take it out, I'll go with what they've done.