Hi I also order the same Rockchip player, but with different box shape at $103 shipped. The spec is exactly the same but without bluetooth and 2.4ghz builtin, and no hdmi cable. Will put some review when i get it.
I think your player displays two portions of internal flash drive which sums up to around 3.xGB. So it really sees the 4GB flash chip; however I don't know why some space is missing.