Bug: updating post slugs in Quick Edit and Classic Editor with a status different from Published

[htdat]

Expected/Desired Behavior

Post slugs can be updated and converted properly. For example, if I add slugs with uppercase characters like MY-post-slug, it will be saved as my-post-slug.

Actual Behavior

Currently, it is not changed and it's still MY-post-slug.

Steps to Reproduce the Problem

Case 1 - Quick Edit

1. Activate only Edit Flow plugin.
2. Add a new post with any status rather than "Published".
3. Go to wp-admin/edit.php, and try to edit the post above with Quick Edit.
4. Try to change the slug to something like MY-post-slug.
5. Reload wp-admin/edit.php, the slug is still MY-post-slug.

Case 2 - Classic Editor

1. Activate only Edit Flow and Classic Editor plugins.
2. Add a new post with any status rather than "Published".
3. Try to edit the post above in the Classic Editor.
4. Try to change the slug to something like MY-post-slug, and save this post.
5. Though the Classic Editor, it's showing all lower cases my-post-slug, in the DB, it's still showing MY-post-slug. This can be checked through Quick Edit in wp-admin/edit.php too.

If I disable Edit Flow or specifically module Custom Statuses (see #633 (comment)), with any status, the slug will be saved with my-post-slug correctly.

(Optional) Additional notes

Tested with WordPress 5.7 and only Edit Flow 0.9.6
Reported from https://wordpress.org/support/topic/slug-does-not-work-for-draft-mode-categories/. They mentioned:

Before the recent WordPress updates all was fine. Now I see that the “slug” for the page or post title does not work.

This support topic was created on Oct 25, 2020. Based on https://wordpress.org/download/releases/, it seems the issue started happening since WordPress 5.5 (released in Aug 2020).

[htdat]

More specifically, in wp-admin/admin.php?page=ef-settings, if I disable the Custom Statuses module, this issue no longer exists.

I've found out that this issue also happens with Classic Editor though there is no issue with Gutenberg (Block Editor). Updated this issue's description and title.

Looks like this is a regression of this PR #575