Clara BW Custom dictionary never sticks as the default

Hi all,

I'm trying to get a custom Spanish–English dictionary to be the default for look-ups in my Spanish books instead of Kobo's built-in one, and I can't make it stick on my Clara BW (firmware 4.45.23684).

Here's the odd part. If I pick one of Kobo's own built-in dictionaries from the dropdown (say English–Turkish), the device happily remembers it as the default for that book. But when I pick my custom dictionary, the choice is never saved. The next look-up jumps straight back to the built-in same-locale dictionary, so I have to re-select it every single time. And if I delete the built-in Spanish–English so only my custom one is left, it just says there's no dictionary for the word.

I also tried dropping the custom file straight into .kobo/dict to replace the built-in. That does make it the default, but Kobo overwrites it with the official one on every sync, and the read-only trick does nothing on this firmware.

So: is there a patch known to work on Clara BW / 4.45.23684 that stops sync from overwriting dictionaries, or that makes a custom dictionary win over the built-in of the same language? Or any reliable manual way to make a custom dictionary stick as the default on current firmware? Happy to share logs or my folder contents if it helps. Thanks!