Disconnected serial console runs out of buffer

When running a guest with both a graphics device and a console device, after a certain amount of text is output to the console, the guest can lock up printing text to the serial console until a connection is made to it using 'virsh console domain'. Upon connecting, the machine immediately unlocks. In this case, the guest has a postgres server that regularly reloads it's configuration and will eventually lock up on the reload, displaying on the console a message similar to:

BUG: soft lockup - CPU#0 stuck for 94393s! [postgresql-8.3:4975]

In this situation I used a while loop running puppet (which is what causes the postgres reload) to reproduce the problem after I suspected this was the case.

----- Host:
Ubuntu 8.10 / intrepid / x86_64

Linux virt11 2.6.27-7-generic #1 SMP Thu Oct 30 04:12:22 UTC 2008 x86_64 GNU/Linux

ii kvm 1:72+dfsg-1ubuntu6 Full virtualization on i386 and amd64 hardware
ii libvirt-bin 0.4.4-3ubuntu3 the programs for the libvirt library

----- Guest:
Ubuntu 8.10 / intrepid / x86_64

Linux stage-util01 2.6.27-7-server #1 SMP Tue Nov 4 20:16:57 UTC 2008 x86_64 GNU/Linux

    <console type='pty'>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' listen='127.0.0.1'/>