Setting tabindex makes other form elements inaccessible to keyboard users.

If remember_me_form_alter() the username, password, remember me and form actions are given tabindex attributes with a value of 1.

I'm not sure why this was ever really needed, as the checkbox gets put in the right place in the form anyway so it's all navigable quite happily via keyboard?

Anyway, unless there's a really good reason why this is required, I'd say it shouldn't be in the module. Messing around with the natural tabbing order of the page is generally considered bad practice unless you really know what you're doing and have a very controlled environment. It's quite an invasive behavioural change.

In our case, we've got other form elements on that form itself which don't also get tabindex added, which makes for a really unpredictable tabbing behaviour. I'll not explain but it essentially makes the other form elements inaccessible (not strictly speaking, but it really messes up the UX for keyboard users).

Patch to follow!