Flashing VA0 bios only works for the second time

[MastaG]

Dear SWAT,

I have a VA0 Dreamcast modded with pico-psu, CF-card reader and piggy-back bios.
I've put some games on my 256GB CF-card and it works like a charm.
Loading times are much much faster.

Now here's what I did.

- I cloned the latest pre-compiled dreamshell release from here: https://github.com/DC-SWAT/DreamShell/tree/master/build
- I've burned this into a selfboot disc (took me a few burns before I figured the binary had to be scrambled lol)
- I've also placed the build files on my FAT32 formatted CF-card in the "DS" directory (without scrambling or touching any of the files)

For the piggy-back bios I'm using the mx29f161 chip and I pretty much followed this image:
https://imgur.com/a/yMH27
Original chip:
- leg 12 lifted and connected to leg 23 using 10k resistor
- everything else connected
mx29f161
- leg 1 lifted and connected to leg 7 of the chip above the bios
- leg 12 lifted and connected to leg 44 using 10k ohm resistor
- leg 44 lifted and connected to leg 23
- all other legs joined, INCLUDING PIN 23

I have the switch set to the original bios and after booting the disc, I change the switch to my piggy back chip.
Now when I try to flash a bios, doesn't matter which one.. it will always fail the first time.
I get some error during erasing.
Then the second time it will work fine.

I've flashed the boot_loader_devkit.bios like 10 times now.. and each time it'll fail the first time, and succeed the second time.

Also it'll work just fine, because my Dreamcast will boot from the piggy-back chip without issues and then load DreamShell from my CF-card without problems.

Any idea why flashing will always fail the first time?