nat network issue

[12bmup]

VirtualBox 4.3.8. Windows 8 host. RHEL 6.5 (and RHEL7 beta) guest. When I use "--nic1 nat" I can transfer files to and from the guest without a problem. If I use "--nic1 natnetwork" I can download large files but when I try to upload I get a broken pipe error. I had this problem with VBox 4.3.6 as well.