The replacement Pi 2 B is behaving in exactly the same way.
So either:
a) I bought a cheap Pi with the same fault
b) There's something wrong with the way I'm populating the SD Card
The files on the SD card are:
Directory of D:\
29/04/2018 16:15 17,932 bootcode.bin
29/04/2018 16:15 302 BUILD-DATA
29/04/2018 16:15 8,172 CHANGELOG.txt
29/04/2018 16:15 2,250 INSTRUCTIONS-README.txt
29/04/2018 16:15 2,572,664 recovery.img
29/04/2018 16:15 112 recovery.cmdline
29/04/2018 16:15 633,252 recovery.elf
29/04/2018 16:15 23,388,160 recovery.rfs
29/04/2018 16:15 0 RECOVERY_FILES_DO_NOT_EDIT
29/04/2018 16:15 2,644,576 recovery7.img
29/04/2018 16:15 29 RELEASE.PilotAware.txt
29/04/2018 16:15 9,728 riscos-boot.bin
29/04/2018 16:15 <DIR> defaults
29/04/2018 16:15 <DIR> os
29/04/2018 16:15 <DIR> overlays
29/04/2018 16:15 14,010 bcm2708-rpi-b.dtb
29/04/2018 16:15 14,273 bcm2708-rpi-b-plus.dtb
29/04/2018 16:15 15,356 bcm2709-rpi-2-b.dtb
29/04/2018 16:15 15,992 bcm2710-rpi-3-b.dtb
16 File(s) 29,336,808 bytes
3 Dir(s) 15,763,800,064 bytes free