Fixed upstream:
commit 952ab4c993b88a324c5910346efa4e75a72293b7
Author:     Ján Tomko <jtomko>
CommitDate: 2013-12-06 15:00:16 +0100

    Add qxl ram size to ABI stability check
    
    55bfd02 added a 'ram' attribute for qxl video devices
    but didn't update the ABI check.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1035123

git describe: v1.2.0-63-g952ab4c

Tested pass with:
libvirt-0.10.2-32.el6.x86_64

Steps:
1.Prepare a guest,set the Display as "Spice" and Video as "QXL".
2.Boot the guest.
3.Use virsh dumpxml to get the xml of the guest.
# virsh dumpxml mig > mig.xml

4.Change the ram value of video:eg:change ram from '65536' to '65535'
change xml from:
      <model type='qxl' ram='65536' vram='65536' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
to:
      <model type='qxl' ram='65535' vram='65536' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>

5.Do migrate,error shows:
# virsh migrate --live mig qemu+ssh://$ip/system --xml mig.xml
error: unsupported configuration: Target video card ram 65535 does not match source 65536

Refer to the above comments,move the bug to VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2014-1374.html