On looking at your completed tasks I can see that you have 2 GPU's; a GTX460 and a GT440:

<core_client_version>6.13.1</core_client_version>
<![CDATA[
<stderr_txt>
# Using device 1
# There are 2 devices supporting CUDA
# Device 0: "GeForce GTX 460"
# Clock rate: 1.66 GHz
# Total amount of global memory: 1073283072 bytes
# Number of multiprocessors: 7
# Number of cores: 56
# Device 1: "GeForce GT 440"
# Clock rate: 1.76 GHz

The details shows that both GPU's are being used interchangeably by the same task:
# Using device 1
# There are 2 devices supporting CUDA
# Device 0: "GeForce GTX 460"
# Clock rate: 1.66 GHz
# Total amount of global memory: 1073283072 bytes
# Number of multiprocessors: 7
# Number of cores: 56
# Device 1: "GeForce GT 440"
# Clock rate: 1.76 GHz
# Total amount of global memory: 1073414144 bytes
# Number of multiprocessors: 2
# Number of cores: 16
MDIO: cannot open file "restart.coor"
# Using device 0

I expect you were running another task at the same time and the tasks swapped cards after work was suspend and resumed (system using >25%, you have deselected 'use GPU when computer is in use', you used snooze, or restarted the system/Boinc).

http://www.gpugrid.net/results.php?hostid=104181

That suggests you have 2 tasks in progress.
What do the logs say?
Have you tried restarting your system?