am335x boneblack memory size and dtb: is memory live patched?

Lately i've been trying to track down a panic i hit when i pass the "mem=256M" option to a 3.16 kernel on a bleaglebone black, and i noticed this:

dtc -I dtb ./arch/arm/boot/dts/am335x-boneblack.dtb
...

        memory {
                device_type = "memory";
                reg = <0x80000000 0x10000000>;
        };

...

that's 256M of memory while the beaglebone black has 512M, does it mean the dtb is live patched (by u-boot?) before being passed to the kernel?

bye,
p.