[libvirt] libvirt, XEN, bridged network and arp

Hi, Ive got a severe networking problem over here: When I boot up my machine (debian lenny) using virsh 0.4.4 on an debian etch, a new virtual eth device (something like vif97.0) is assigned to that machine and that device is attached to my bridge virbr1. That is fine. Not so fine is the fact, that no arp packages come over to my bridge for about 5 seconds or so. During that time I can see a lot of arp-who-has on vifXX.0 but nothing on virbr1 so there are no answers and the result is my guest machine not mounting nfs directories on boot. After some time (e.g. after login) networking works fine - but thats definitely too late - I need those directories mounted on boot. Is there a way to fix that?