syncthing: Adding UPnP mapping which already exists causes UPnP logic to fail

I have 2 installs in the same LAN, the first one is v 0.11.5 on an ARM machine, the second is v 0.11.3 on an OSX machine, and both give me the same error, which is the one on the title.

I ran the trace on the ARM machine but the result is the same on OSX, this is the link to the entire STTRACE=upnp log http://hastebin.com/ariwepeyol.xml and following there’s the relevant bits:

[RHG44] 16:50:23 DEBUG: Handling UPnP response:

HTTP/1.1 200 OK
Cache-Control: max-age=3600
ST: urn:schemas-upnp-org:device:InternetGatewayDevice:1
USN: uuid:...::urn:schemas-upnp-org:device:InternetGatewayDevice:1
EXT:
Server:  Unspecified, UPnP/1.0, Unspecified
Location: http://192.168.1.1:56688/rootDesc.xml


[RHG44] 16:50:24 DEBUG: [http://192.168.1.1:56688/rootDesc.xml] Found urn:schemas-upnp-org:service:WANIPConnection:1 with URL http://192.168.1.1:56688/ctl/IPConn
[RHG44] 16:50:24 DEBUG: [http://192.168.1.1:56688/rootDesc.xml] Found urn:schemas-upnp-org:service:WANPPPConnection:1 with URL http://192.168.1.1:56688/ctl/PPPConn
[RHG44] 16:50:24 DEBUG: UPnP discovery result 824ff22b-8c7d-41c5-a131-4494fceaf65e with services:
[RHG44] 16:50:24 DEBUG: * [urn:upnp-org:serviceId:WANIPConn1] http://192.168.1.1:56688/ctl/IPConn
[RHG44] 16:50:24 DEBUG: * [urn:upnp-org:serviceId:WANPPPConn1] http://192.168.1.1:56688/ctl/PPPConn
[RHG44] 16:50:32 DEBUG: Discovery for device type urn:schemas-upnp-org:device:InternetGatewayDevice:1 on eth0 finished.
[RHG44] 16:50:32 DEBUG: Discovery for device type urn:schemas-upnp-org:device:InternetGatewayDevice:2 on eth0 finished.
[RHG44] 16:50:32 DEBUG: Discovery for device type urn:schemas-upnp-org:device:InternetGatewayDevice:1 on wlan0 finished.
[RHG44] 16:50:32 DEBUG: Discovery for device type urn:schemas-upnp-org:device:InternetGatewayDevice:2 on wlan0 finished.
[RHG44] 16:50:32 DEBUG: SOAP Request URL: http://192.168.1.1:56688/ctl/IPConn
[RHG44] 16:50:32 DEBUG: SOAP Action: 
[RHG44] 16:50:32 DEBUG: SOAP Request:

<?xml version="1.0" ?>
    <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
    <s:Body><u:AddPortMapping xmlns:u="urn:schemas-upnp-org:service:WANIPConnection:1">
    <NewRemoteHost></NewRemoteHost>
    <NewExternalPort>54861</NewExternalPort>
    <NewProtocol>TCP</NewProtocol>
    <NewInternalPort>22000</NewInternalPort>
    <NewInternalClient>192.168.1.60</NewInternalClient>
    <NewEnabled>1</NewEnabled>
    <NewPortMappingDescription>syncthing-0</NewPortMappingDescription>
    <NewLeaseDuration>0</NewLeaseDuration>
    </u:AddPortMapping></s:Body>
    </s:Envelope>

[RHG44] 16:50:33 DEBUG: SOAP Response:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<s:Body>
<s:Fault>
<faultcode>s:Client</faultcode>
<faultstring>UPnPError</faultstring>
<detail>
<UPnPError xmlns="urn:schemas-upnp-org:control-1-0">
<errorCode>718</errorCode>
<errorDescription>ConflictInMappingEntry</errorDescription>
</UPnPError>
</detail>
</s:Fault>
</s:Body>
</s:Envelope>