You sure you updated it all the way (and do not participate in beta previews)? I had a workaround (fatpatch) but it did not work for everyone either. It was my understanding that MS had fixed this issue so I removed the attachments...
Really not sure what Kobo is doing.
The 4.x firmware has moved the firmware reset confoundery from the user partition to the MBR.
Code:
#hexdump -C -n 512 /dev/mmcblk0
-00000130 00 00 00 1b df 05 a5 01 00 00 00 00 00 00 00 00 |................|
+00000130 00 00 00 a1 8e 0c 3c 02 00 00 00 00 00 00 00 00 |......<.........|
Not sure if they also actively fix the user partition somehow while updating firmware.
The 4.x firmware works on the H2O so it might be worth a try (but it gave me battery issues).