slow (/2) MMC/SD clocking

I have a question about the MMC/SD clock. My board has the following clock settings:

ARM9_0: GEL Output: ---------------------------------------------
ARM9_0: GEL Output: | PLL0 Information |
ARM9_0: GEL Output: ---------------------------------------------
ARM9_0: GEL Output:
ARM9_0: GEL Output: PLL0_SYSCLK1 = 312 MHz
ARM9_0: GEL Output: PLL0_SYSCLK2 = 156 MHz
ARM9_0: GEL Output: PLL0_SYSCLK3 = 26 MHz
ARM9_0: GEL Output: PLL0_SYSCLK4 = 78 MHz
ARM9_0: GEL Output: PLL0_SYSCLK5 = 104 MHz
ARM9_0: GEL Output: PLL0_SYSCLK6 = 312 MHz
ARM9_0: GEL Output: PLL0_SYSCLK7 = 52 MHz

Now I set the MMCCLK register to 0x0101. This should result in an 37.5MHz clock on the SD card.

If I measure the clock (MMCSD0_CLK) with the oscilloscope I only get 19MHz. Also if I set the MMCCLK register to another value, the measured clock is half of the required one.

Measuring SYSCLK2 on the DDR ram shows 150MHz, so the PLL settings seems to be right.

Thanks for any suggestions. 

regards

Armin