emmc boot with sd card in slot1

I ran into a fun problem where my pyra doesn't seem to boot when there's an sd card in slot 1 that doesn't have a bootloader.

(dd'ed 50mb of zeros onto the card first, then created a fat32 partition)

I installed uboot on the emmc, and that boots when the card is removed (after having pressed power for 8 seconds to shut it down completely, then power again to start it. it seems to get stuck. It does pull 0.5A from the usb socket).

Is this an issue on the other prototypes as well, or is this part of the "wrong resistor that puts the cpu in debug mode" problem that this older prototype apparently has ?