TLC5954: Problem writing control registers

We are using the TLC5954 driver to create a matrix display.  We can successfully control the LEDs by writing the bitmap to the On/Off data register and can control the LED brightness by writing values to the control registers.  The problem is arising when we write new brightness values to the control registers while the display is active.  Specifically, when there is a relatively large number of LEDs "on" (>25-30) and new values are written to the BC registers, some of the LEDs turn off.  If the number of LEDs "on" is relatively small (<14) we do not see this happen.  Essentially, the larger the number of LEDs on when the write of new brightness values happens, the more LEDs turn off.  If the bitmap is re-written to the On/Off data register, everything is fine.