That is the energy saving clock. Just tax it with some serious work like atitool or do something simple like taking a window and move it around on the screen a lot. You will notice the clocks will quickly jump to the default clocks whatever they are with your GPU.
There are usually 3 energy saving settings.
Full Speed.
Medium like half clock
and minimum usually as low as it gets without problems. About 100 Mhz usually. If it is idle just showing the desktop it will stay at the minimum clock.