Net Render - slaves is added to slaves' list many times

Hi, I use 4 PCs (windows 7,8) with 14 GPUs for rendering simple animation. I use Net Render. After some time of rendering, one of slaves is added to slaves’ list many times and all frames are dispatched to the slaves’ copies.

When I restart slave and all dispatched frames, the situation repeats.

When I restart all 4 PCs masters, slaves and client, it works correctly until the problem happens again.

E:\BLENDER\blender-2.71-windows64\blender.exe -b master.blend --addons netrender -a -noaudio -nojoystick

one of slave.bat
E:\BLENDER\blender-2.71-windows64\blender.exe -b slave.blend --addons netrender -a -noaudio -nojoystick

Please, help!