Text area using Better Formats interfering with WYSIWYG editor after Drupal 6.26 update

After upgrading from Drupal 6.25 to 6.26, text areas using Better Formats are not loading the WYSIWYG editor or any Better Formats settings (e.g. the input format switcher or hiding the formatting help link). I've used Better Formats for years with no problems, and it had been working fine on this install up until now.

Apologies if this seems long, but I wanted to be thorough on my report:

• This only affects text areas configured as "text area using Better Formats." Better Formats is working properly on regular formatted text areas.
• All users but user1 see a plaintext area with a link to "formatting help." No input filters are displayed. Basically it's acting as if it's a plaintext text area. User1 is unaffected, presumably because its all-access permission overrides anything Better Formats does.

Because of the above, I'm fairly certain this is a Better Formats thing and not related to the WYSIWYG module, or the CKEditor that I'm using. In any case, reinstalling those had no effect.

No changes have been made to the Better Formats permissions settings or the input filter defaults since it previously worked. However, I confirmed that these were set correctly: users of a given role have an input filter with WYSIWYG editors as default, and permission to use those filters, and the Better Formats permissions are enabled to allow them to switch. Even if somehow those were messed up, Better Formats is quite clearly set to hide the "Formatting help" link for these users, and it's getting displayed, so clearly Better Formats isn't being triggered.

Digging into the code, I can make comparisons between what's loaded for user1 and all other users on these text areas:

• ckeditor.js is loaded in both cases. However, the language script, en.js, is not loaded for anyone but user1. Presumably this is because CKEditor thinks there are no formatted text areas.
• Similarly, the text area itself is missing all of the CKEditor tags and classes on it. Again, I'm pretty sure this is because CKEditor doesn't think the field is a formatted text area.

I would consider going the route of disabling Better Formats entirely, but as these content types have the Better Formats-enabled text areas, that would actually mean migrating data to regular text areas, which I definitely don't want to do.

Has anyone else experienced Better Formats interfering with their WYSIWYG editors?