Perforce Plugin on OSX "Client unknown"

The perforce plugin on OSX appears to be quite confused.

Using P4CONFIG, values are read correctly when using Test Connection button, but error reported is "Client unknown"

When I press the Test Connection button, it seems to attempt to launch P4V unsuccessfully - the app is launched to my tray, but no main window is ever created.

Path to P4 executable: /Applications/p4vc
Path to P4V executable: /Applications/p4v.app/Contents/MacOS/p4v

Output from p4vc -V:

Perforce - The Fast Software Configuration Management System.
Copyright 1995-2015 Perforce Software.  All rights reserved.
Rev. P4VC/MACOSX107X86_64/2014.3/1007540 (2015/02/18).

Output from p4.output:

18:40:28 info
18:40:28
ErrCode=0
StdOut:------------
unknown command
error : unknown


        help          Print the requested help message
        branchmappings   Shows list of branch mappings
        branches         Same as branchmappings. Shows list of branch mappings
        diff             Shows diff dialog
        groups           Shows list of groups
        branch           Show/Edit branch
        change           Show/Edit change
        client           Same as workspace. Show/Edit workspace
        workspace        Show/Edit workspace
        depot            Show/Edit depot
        group            Show/Edit group
        job              Show/Edit job
        label            Show/Edit label
        user             Show/Edit user
        jobs             Shows list of jobs
        labels           Shows list of labels
        pendingchanges   Shows list of pending changes
        resolve          Launches resolve dialog
        revisiongraph    Shows revision graph
        revgraph         Same as revisiongraph. Shows revision graph
        streamgraph      Shows stream graph pane
        streams          Shows list of streams
        submit           Launches submit dialog
        submittedchanges Shows list of submitted changes
        timelapse        Shows timelapse view
        timelapseview    Same as timelapse. Shows timelapse view
        tlv              Same as timelapse. Shows timelapse view
        users            Shows list of users
        workspaces       Shows list of workspaces
        clients          Same as workspaces. Shows list of workspaces
        shutdown         Shut downs the p4v service


StdErr:------------


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