qemu 2.5 network model rtl8139 collisions Ubuntu 16.04.2 LTS

When I use NIC model rtl8139, I have a lot collisions and very low transfer.
I tested that with brctl and Open vSwitch, because I thought that was a vSwitch issue. 
When I change NIC model to virtio all works as expect.

Host: Ubuntu 16.04.2 LTS
Guest: Ubuntu 14.04.5 LTS - affected
Guest: Ubuntu 16.04.2 LTS - not affected

QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.10)