Create a filter with the "Match all messages" bullet selected.

Back up filters through the "Backup filters" button.

Deleted all filters.

Restore filters from the backup created above. 

The filter created with the "Match all messages" bullet selected now has the
"Match all of the following" bullet selected, and the first filter is [Subject]
[contains] [ ] (the matching criteria is empty).

Can you send me the exported file directly? (don't attach it here)

(In reply to comment #1)
> Can you send me the exported file directly? (don't attach it here)
> 

I've sent two emails. The first contains the backup of the local folders
filters. The second has the backup of the account filters.

Just to be sure, are you waiting on something from me?

I know that last set of filters I sent were sent to the wrong address, and I
had to resend them. Since then I've heard nothing.