Cannot use multiple displays on Mac OS X

[Stereo]

What steps will reproduce the problem?

1. Connect a second display to your mac
2. Open e.g. a relation editor, and move that window to the second screen
3. Edit the map

What is the expected result?

Relation editor can stay on the second screen

What happens instead?

Window moves back to the first screen, becomes invisible

Please provide any additional information below. Attach a screenshot if possible.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-06-04 17:28:58 +0200 (Sat, 04 Jun 2016)
Build-Date:2016-06-04 15:31:27
Revision:10327
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10327 en_GB) Mac OS X 10.11.5
Memory Usage: 991 MB / 3641 MB (422 MB allocated, but free)
Java version: 1.8.0_91-b14, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
VM arguments: [-Djava.library.path=/Applications/JOSM.app/Contents/MacOS, -DLibraryDirectory=${HOME}/Library, -DDocumentsDirectory=${HOME}/Documents, -DApplicationSupportDirectory=${HOME}/Library/Application Support, -DCachesDirectory=${HOME}/Library/Caches, -DSandboxEnabled=false, -Dapple.laf.useScreenMenuBar=true, -Dcom.apple.macos.use-file-dialog-packages=true, -Dcom.apple.macos.useScreenMenuBar=true, -Dcom.apple.mrj.application.apple.menu.about.name=JOSM, -Dcom.apple.smallTabs=true]
Dataset consistency test: No problems found

Plugins:
- AddrInterpolation (32309)
- CommandLine (32329)
- DirectDownload (32309)
- DirectUpload (32329)
- FixAddresses (32309)
- HouseNumberTaggingTool (32309)
- ImportImagePlugin (32158)
- ImproveWay (1452443304)
- Mapillary (32158)
- OSMRecPlugin (32158)
- OpeningHoursEditor (32309)
- PicLayer (32329)
- RoadSigns (32309)
- ShapeTools (1000)
- alignways (32326)
- apache-commons (32309)
- apache-http (32309)
- areaselector (271)
- auto_tools (1466178229)
- buildings_tools (32309)
- cadastre-fr (32329)
- conflation (0.2.0)
- contourmerge (1014)
- download_along (32309)
- ejml (32309)
- geotools (32309)
- gson (32309)
- imagery-xml-bounds (32158)
- imagery_offset_db (32329)
- importvec (32158)
- josm-geojson (31245)
- jts (32311)
- livegps (32309)
- log4j (32309)
- mapdust (32329)
- merge-overlap (32309)
- namemanager (32309)
- opendata (32158)
- pdfimport (32309)
- pt_assistant (32540)
- public_transport (32309)
- public_transport_layer (32309)
- reverter (32309)
- scripting (30723)
- splinex (32309)
- surveyor (32329)
- tageditor (32309)
- terracer (32309)
- turnlanes (32309)
- turnrestrictions (32158)
- undelete (32309)
- utilsplugin2 (32158)

Tagging presets:
- http://osmtools.de/josm/steps.xml
- https://josm.openstreetmap.de/josmfile?page=Presets/BicycleJunction&preset&zip=1
- https://josm.openstreetmap.de/josmfile?page=Presets/Golf_Course&zip=1
- https://josm.openstreetmap.de/josmfile?page=Presets/Historic_Stone&zip=1
- https://josm.openstreetmap.de/josmfile?page=Presets/LaneAttributes&preset&zip=1
- https://josm.openstreetmap.de/josmfile?page=Presets/NewTags&zip=1
- https://josm.openstreetmap.de/josmfile?page=Presets/Towers&zip=1

Map paint styles:
- http://maps.openstreetmap.ie/josm/townland.mapcss
- https://github.com/GlassOceanos/indoor-JOSM-style/archive/master.zip
- https://github.com/simon04/coloured-addresses.mapcss/raw/master/dist/coloured-addresses.mapcss
- https://josm.openstreetmap.de/josmfile?page=Styles/AddressValidator&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/BesideTheRoad_Speed&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Coloured_Streets&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Coloured_Suburb&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Cycleways&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Lane_and_Road_Attributes&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/LessObtrusiveNodes&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Lit&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Maxspeed&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Modified&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Noname&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/PTStops&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/ParkingLanes&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Power&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/PowerMapping&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/PublicTransport&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/SlovakiaBicycleRoutes&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Surface&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Surface-DataEntry&style&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/TreeCrownDiameter&style&zip=1

Last errors/warnings:
- E: Failed to locate image ''

[Stereo]

Closed as duplicate of #12150.