oclHashcat for AMD v1.30 slow with "mask"

Hi.

In case you run a brute force with mask, speed decreases.
oclHashcat32.exe -m 0 -a 3 8fa1c84f6XXXX38ccXXXXf04274a0c52 ?a?a?a?a?a?a?a?a?a?a?a?a
Speed.GPU.#1...: 1108.5 MH/s

oclHashcat32.exe -m 0 -a 3 8fa1c84f6XXXX38ccXXXXf04274a0c52 ?a?a?a?a?a?a?a?akeys
Speed.GPU.#1...: 992.8 MH/s

oclHashcat32.exe -m 0 -a 3 8fa1c84f6XXXX38ccXXXXf04274a0c52 keys?a?a?a?a?a?a?a?a
Speed.GPU.#1...: 10220.0 kH/s



Why does my search mask keys?a?a?a?a?a?a?a?a well as speed decreases?
Thank you for your help.
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E6600 + ATI5670