MacOS System Preferences > General > Prefer tabs > Always causes certain modals to open as tabs and break JOSM

[rideearthtom]

What steps will reproduce the problem?

1. Set MacOS System Preferences > General > Prefer tabs > Always
2. Open any dataset
3. Open relation editor

What is the expected result?

Relation editor opens and works normally

What happens instead?

Relation editor opens as a tab and disables all input (trackpad/keyboard) for the entire app, including menu bar, necessitating force quit.

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

I use JOSM professionally and have been unable to work for several weeks since updating to the latest version of MacOS, in which several default system preferences changed. There appears to be some kind of strange issue caused by this specific tab/window setting. I've now diagnosed the cause and left this ticket open for a fix to be implemented.

Revision:17580
Build-Date:2021-03-18 15:54:45

Identification: JOSM/1.5 (17580 en_GB) Mac OS X 10.16
OS Build number: macOS 11.2.3 (20D91)
Memory Usage: 328 MB / 8192 MB (104 MB allocated, but free)
Java version: 16+36, Azul Systems, Inc., OpenJDK 64-Bit Server VM
Look and Feel: com.apple.laf.AquaLookAndFeel
Screen: Display 69731840 1280×800 (scaling 2.00×2.00)
Maximum Screen Size: 1280×800
Best cursor sizes: 16×16→16×16, 32×32→32×32
VM arguments: [-Djpackage.app-version=17580, --add-exports=java.desktop/com.apple.eawt=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.plugins.jpeg=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.spi=ALL-UNNAMED, --add-opens=java.base/java.lang=ALL-UNNAMED, --add-opens=java.base/java.nio=ALL-UNNAMED, --add-opens=java.base/jdk.internal.loader=ALL-UNNAMED, --add-opens=java.base/jdk.internal.ref=ALL-UNNAMED, --add-opens=java.desktop/javax.imageio.spi=ALL-UNNAMED, --add-opens=java.desktop/javax.swing.text.html=ALL-UNNAMED, --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED, -Djpackage.app-path=/Applications/JOSM.app/Contents/MacOS/JOSM]

[rideearthtom]

Update: I've identified the cause of the problem, and I believe it should be handled by JOSM, so am keeping this ticket open. Replicate it by changing System Preferences > General > Prefer tabs to Always. Reverting to Never resolves the symptom but not the underlying issue.