Booting Stretch (debian 9.3) from SD card redirects to emmc?

When I boot Stretch with the /boot/uEnv.txt containing this:

dtb=am335x-boneblack-emmc-overlay.dtb

Then the SD card will start booting, all the LEDs pause, then restart and it boots from emmc instead! Is this a bug?

My emmc is loaded with Jessie, so I can easily tell when this happens.

Also, this doesn’t appear to happen on Jessie.

uEnv.txt:

`
#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.9.78-ti-r94

#uuid=

this one boots to emmc even when starting from SD card

#dtb=am335x-boneblack-emmc-overlay.dtb

dtb=am335x-boneblack-uboot.dtb

###U-Boot Overlays###

###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays

###Master Enable

enable_uboot_overlays=1