Pwauth problem with local users

Please help us by providing the following info. Before posting please also check the pinned "Known issues" threads and make sure that you're running the latest available version for your oC release: https://owncloud.org/changelog/

Steps to reproduce
1. Enable Unix authentication addon (https://apps.owncloud.com/content/show.php?content=148406)
2. Create local unix user with capital letter, and assign password
3. Try to login with unix user on Owncloud logon screen

Expected behaviour
User should be logged in

Actual behaviour
User gets "Wrong password. Reset it?" message when username has a capital letter, works fine when username is all lowercase

Server configuration
Operating system: NETGEAR ReadyNAS OS 6.6.0 (Debian Jessie Derivative)
Web server: Apache 2.2.31
Database: MySQL 5.5.53-0+deb8u1
PHP version: 5.6.24-0+deb8u1.netgear1
ownCloud version (see ownCloud admin page): ownCloud 9.1.3 (stable)
Updated from an older ownCloud or fresh install: Fresh install
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): External storage enabled (local), external authentication (unix).

ownCloud log (data/owncloud.log)

Please paste possible errors in the following code block

Debug	OC\Files\Cache\Scanner	!!! Path '' is not accessible or present !!!	2017-01-04T19:07:34+00:00
Debug	OC\Files\Cache\Scanner	!!! Path '' is not accessible or present !!!	2017-01-04T19:07:34+00:00
Warning	core	Login failed: 'Paul' (Remote IP: '192.168.59.254')	2017-01-04T19:01:24+00:00
Debug	DeleteOrphanedSharesJob	0 orphaned share(s) deleted	2017-01-04T18:59:51+00:00
Info	no app in context	Invalidating tokens older than 2017-01-03T18:58:08+00:00	2017-01-04T18:58:08+00:00
Debug	core	OC_Image->fixOrientation() Orientation: 1	2017-01-04T18:53:07+00:00
Debug	core	Generating preview for "/Photos/Paris.jpg" with "OC\Preview\JPEG"	2017-01-04T18:53:07+00:00
Debug	core	OC_Image->fixOrientation() Orientation: 1	2017-01-04T18:53:06+00:00
Debug	core	Generating preview for "/Photos/San Francisco.jpg" with "OC\Preview\JPEG"	2017-01-04T18:53:06+00:00
Debug	core	OC_Image->fixOrientation() Orientation: 1	2017-01-04T18:53:06+00:00
Debug	core	Generating preview for "/Photos/Squirrel.jpg" with "OC\Preview\JPEG"	2017-01-04T18:53:06+00:00
Debug	files_skeleton	copying skeleton for testuser from /apps/owncloud/web/core/skeleton to /testuser/files/	2017-01-04T18:50:18+00:00
Debug	OC\Files\Cache\Scanner	!!! Path '' is not accessible or present !!!	2017-01-04T18:50:11+00:00
Debug	OC\Files\Cache\Scanner	!!! Path '' is not accessible or present !!!	2017-01-04T18:50:11+00:00
Debug	OC\Files\Cache\Scanner	!!! Path '' is not accessible or present !!!	2017-01-04T18:50:11+00:00
Warning	core	Login failed: 'Paul' (Remote IP: '192.168.59.254')	2017-01-04T18:31:24+00:00
Warning	core	Login failed: 'Ben' (Remote IP: '192.168.59.254')	2017-01-04T18:29:10+00:00
Warning	core	Login failed: 'Paul' (Remote IP: '192.168.59.254')	2017-01-04T18:29:01+00:00
Warning	core	Login failed: 'Paul' (Remote IP: '192.168.59.254')	2017-01-04T18:28:54+00:00

Integrity status for oC9+

No errors have been found.