Rapid tremendous memory hog when using -net nic,vlan=0 -net user,vlan=0

A rapid tremendous memory hog is occuring when I use -net nic,vlan=0 -net user,vlan=0. Tested with QEMU 2.8.0 & 2.9.0 in Gentoo. All available memory (8GB) + swap (over 20GB) is exhausted very rapidly. 

This bug is possibly related to 
https://bugs.launchpad.net/qemu/+bug/1310714 
and maybe to
https://bugs.launchpad.net/qemu/+bug/1288620

The bug IS present wheh I use -net nic,vlan=0 -net user,vlan=0 (tested with no model and model=e1000 and model=virtio, with all these the bug is present)

The bug is NOT present with I use this:
-netdev type=user,id=mynet0 -device virtio-net-pci,netdev=mynet0

I tested this bug only using windows guests (Windows XP & Windows 8).