Named parser cannot be referenced multiple times

[presidento]

The syslog-ng cannot start (with message Error initializing message pipeline;) if a named parser is referenced multiple times.

Version of syslog-ng

syslog-ng 3.9.1
Installer-Version: 3.9.1
Revision: 
Module-Directory: /home/matefarkas/install/syslog-ng/lib/syslog-ng
Module-Path: /home/matefarkas/install/syslog-ng/lib/syslog-ng
Available-Modules: afmongodb,affile,sdjournal,confgen,cryptofuncs,syslogformat,pseudofile,afsocket,afamqp,basicfuncs,afuser,linux-kmsg-format,tfgetent,afprog,kvformat,mod-python,date,graphite,disk-buffer,csvparser,dbparser,add-contextual-data,cef,afstomp,system-source,json-plugin
Enable-Debug: on
Enable-GProf: off
Enable-Memtrace: off
Enable-IPv6: on
Enable-Spoof-Source: off
Enable-TCP-Wrapper: off
Enable-Linux-Caps: off

Steps to reproduce

1. touch etc/hosts.csv
2. Edit syslog-ng.conf
3. Try to start syslog-ng

Configuration

@version: 3.9
parser p_contextual {
    add_contextual_data( database("hosts.csv") selector("${HOST}") );
};
log {
    source{ internal(); };
    parser(p_contextual);
    #parser(p_contextual); # Enable this line and syslog-ng won't start
    destination { file("/dev/null"); };
};

It also fails if the parser is referenced by 2 absolutely different log path.