[U-Boot] CONFIG_SYS_FLASH_USE_BUFFER_WRITE breaks writing with M29W640 parts

i started playing with the CONFIG_SYS_FLASH_USE_BUFFER_WRITE option, and it seems to work fine with an intel strataflash. but when i tried using it with an ST M29W640 part, no writes are ever committed to the flash.

are there any known gotchas with this code before i start poking further ? -mike