Wordpress 4.9 bug with page templates

[bojankr]

Ok, so shortly, custom theme has couple of page templates, all affecting pages only, located in theme template-parts folder (like _s structure).

When I updated Wordpress to 4.9, I can't create page templates anymore, when I add page template, choose unique name, it doesn't show up on page templates list (as tho values, or list of files is cached somehow).

When i rename template name in already existing page-template, it changes it properly in templates list (in page edit).

But, when I rename page-template into (old name: template-example.php) for example: template-newexample.php, i get error:

Warning: file_get_contents(/vagrant/wp-content/themes/mytheme/template-parts/template-example.php): failed to open stream: No such file or directory in /vagrant/wp-includes/class-wp-theme.php on line 1042

as tho it is cached somewhere.
This is happening when I try to rename any page template, not just certain one, and even if that page template isn't used anywhere, it still bugs out

[bojankr]

Screenshot of error

[bojankr]

I want to say, when I reverted back to previous patch (4.8.3), everything worked fine.

[Presskopp]

related (if not duplicate of) #42573

[swissspidy]

Duplicate of #42573.