A fix for this bug was pushed upstream and will be in libvirt-1.1.0. Please see Bug 979290 for more details/discussion:

commit 374c5e4f73577b316fed19bbcefe74b75195eb95
Author: Laine Stump <laine@laine.org>
Date:   Sun Jun 30 14:49:21 2013 -0400

    node device driver: update driver name during dumpxml
    
 
    The node device driver was written with the assumption that udev would
    use a "change" event to notify libvirt of any change to device status
    (including the name of the driver it was bound to). It turns out this
    is not the case (see Comment 4 of BZ 979290). That means that a
    dumpxml for a device would always show whatever driver happened to be
    bound at the time libvirt was started (when the node device cache was
    built).
    
    There was already code in the driver (for the benefit of the HAL
    backend) that updated the driver name from sysfs each time a device's
    info was retrieved from the cache. This patch just enables that manual
    update for the udev backend as well.

Verifying this bug with libvirt-0.10.2-19.el6:

---------------------------------------------
Reproduced with libvirt-0.10.2-18.el64_9:
1. check the pci driver with virsh command nodedev-dumpxml.
# virsh nodedev-dumpxml pci_0000_04_00_0
<device>
  <name>pci_0000_04_00_0</name>
  <parent>pci_0000_00_1e_0</parent>
  <driver>
    <name>e1000</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>4</bus>
    <slot>0</slot>
    <function>0</function>
    <product id='0x107c'>82541PI Gigabit Ethernet Controller</product>
    <vendor id='0x8086'>Intel Corporation</vendor>
  </capability>
</device>

2. check it's driver with kernel command
# readlink -f /sys/bus/pci/devices/0000\:04\:00.0/driver/
/sys/bus/pci/drivers/e1000

3. change the pci's driver to others, such as change from driver e1000 to driver pci-stub
# virsh nodedev-detach pci_0000_04_00_0
Device pci_0000_04_00_0 detached

4. check the driver with kernel command again, it is changed to pci-stub
# readlink -f /sys/bus/pci/devices/0000\:04\:00.0/driver/
/sys/bus/pci/drivers/pci-stub

5. check the driver with virsh command nodedev-dumpxml, it didn't be updated.
# virsh nodedev-dumpxml pci_0000_04_00_0
<device>
  <name>pci_0000_04_00_0</name>
  <parent>pci_0000_00_1e_0</parent>
  <driver>
    <name>e1000</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>4</bus>
    <slot>0</slot>
    <function>0</function>
    <product id='0x107c'>82541PI Gigabit Ethernet Controller</product>
    <vendor id='0x8086'>Intel Corporation</vendor>
  </capability>
</device>

---------------------------------------------
Verfied with libvirt-0.10.2-19.el6:
1. check the pci driver with virsh command nodedev-dumpxml.
# virsh nodedev-dumpxml pci_0000_04_00_0
<device>
  <name>pci_0000_04_00_0</name>
  <parent>pci_0000_00_1e_0</parent>
  <driver>
    <name>e1000</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>4</bus>
    <slot>0</slot>
    <function>0</function>
    <product id='0x107c'>82541PI Gigabit Ethernet Controller</product>
    <vendor id='0x8086'>Intel Corporation</vendor>
  </capability>
</device>

2. check it's driver with kernel command
# readlink -f /sys/bus/pci/devices/0000\:04\:00.0/driver/
/sys/bus/pci/drivers/e1000

3. change the pci's driver to others, such as change from driver e1000 to driver pci-stub
# virsh nodedev-detach pci_0000_04_00_0
Device pci_0000_04_00_0 detached

4. check the driver with kernel command again, it is changed to pci-stub
# readlink -f /sys/bus/pci/devices/0000\:04\:00.0/driver/
/sys/bus/pci/drivers/pci-stub

5. check the driver with virsh command nodedev-dumpxml:
# virsh nodedev-dumpxml pci_0000_04_00_0
<device>
  <name>pci_0000_04_00_0</name>
  <parent>pci_0000_00_1e_0</parent>
  <driver>
    <name>pci-stub</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>4</bus>
    <slot>0</slot>
    <function>0</function>
    <product id='0x107c'>82541PI Gigabit Ethernet Controller</product>
    <vendor id='0x8086'>Intel Corporation</vendor>
  </capability>
</device>

Driver was updated exactly.

So setting 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-2013-1581.html