This parameter is rather confusing. In some places it is defined as 1 and it's mentioned it can be used to overwrite mac address (or env is not writable now) in other places without 1 it says

include/configs/EP1C20.h:#define CONFIG_ENV_OVERWRITE /* Serial change Ok */ include/configs/scb9328.h:#define CONFIG_ENV_OVERWRITE 1 /* env is not writable now */

include/configs/QS823.h:#define CONFIG_ENV_OVERWRITE 1 /* allow overwrite MAC address */

include/configs/PPChameleonEVB.h:#define CONFIG_ENV_OVERWRITE /* Let the user to change the Ethernet MAC addresses */

So, what will be correct for ixdp425? How this parameter can affect reading environment settings from flash?