BUG #15117: Duplicate Primary Key

The following bug has been logged on the website:

Bug reference:      15117
Logged by:          Kyle Kinnear
Email address:      kyle.kinnear@welchallyn.com
PostgreSQL version: 9.6.6
Operating system:   Windows 10 Enterprise - 14393.2035
Description:

Hello,

While running some performance simulations on a test application server
overnight, I came back to some odd errors. I was then able to trace it back
to the primary index of this table being duplicated.

Here is the information for the table, done from an export:

reco_id    modality    user_id    file_name    update_ts    groups_fk
9    4    1    UserPreferences.xml    2018-02-14 21:35:33.122    7
10    4    1    UserPreferences.xml    2018-02-14 21:35:34.903    8
6    0    3    ExMgrUserPreferences.xml    2018-02-08 20:40:59.869    -1
5    255    3    CFDL.XML    2018-02-08 20:41:01.619    -1
3    4    1    UserPreferences.xml    2018-03-09 21:13:54.36817    1
12    0    4    ExMgrUserPreferences.xml    2018-02-14 22:23:10.212115    -1
11    255    4    CFDL.XML    2018-02-14 22:23:11.965623    -1
13    4    4    UserPreferences.xml    2018-02-14 22:23:11.965623    7
16    4    5    UserPreferences.xml    2018-02-14 22:24:43.012535    8
15    0    5    ExMgrUserPreferences.xml    2018-02-14 22:24:41.304534    -1
14    255    5    CFDL.XML    2018-02-14 22:24:43.012535    -1
1    255    1    CFDL.XML    2018-03-09 21:13:54.36817    -1
2    0    1    ExMgrUserPreferences.xml    2018-03-16 14:58:44.621422    -1
2    0    1    ExMgrUserPreferences.xml    2018-03-16 14:58:44.621422    -1