E-Mail notification: no change after template changed

Steps to reproduce
1. As admin, change both email templates for new users (html and plain text) and save; make sure "saved" is shown successfully
2. Configure that new users get an email
3. Create a new user and check received email

Expected behaviour
The email should contain the changes from the template

Actual behaviour
It doesn't - the old template is still used

Server configuration
Operating system: Linux
Web server: Apache
Database: MySSL
PHP version: 7
ownCloud version (see ownCloud admin page): 9.1.2
Updated from an older ownCloud or fresh install: updated
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): no

ownCloud log (data/owncloud.log)

opendir(/tmp): failed to open dir: Permission denied at /www/htdocs/v100266/cloud/lib/private/TempManager.php#188

This error is repeatedly shown.
Seems to be another issue (I'm at all-inkl).

Integrity status for oC9+

No errors have been found.

In case there are no clues - should I file a bug report?

You can set a user defined temp directory in your config/config.php where you have full access.

I suppose you already enabled the debug mode for your logfiles?

tmp dir
So far I've only seen solutions where the php.ini needed to be changed to configure the tmp path (I can't change the php.ini), but now I've found the option for config/config.php. Thanks! That one seems to be fixed, no more errors although the tmp dir is empty. Btw: I've used the basepath from the option datadirectory in the same file, where an absolute path /www/htdocs/.../data is stated, although I don't know where this path is coming from. I thought that owncloud can't read any absolute paths on the shared host.

mail templates
Now I've also set the debug=true and in the admin page I've set What to log to everything.
The mail templates still don't seem to work. I also don't see any new log messages that would indicate the problem.

Last thing to try, update to the latest version 9.1.3 (https://owncloud.org/changelog/#latest9.1) and if this doesn't fix it, report it to the bugtracker.