Join areas action may create "Ways with same position"

[GerdP]

What steps will reproduce the problem?

1. load attached file
2. select the two residential areas
3. Press Shift+J to join the areas

What is the expected result?

A landuse=residential multipolygon where the landuse=forest way is an inner

What happens instead?

A landuse=residential multipolygon with an additinal way as inner. The validator complains
"Ways with same position"

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

Build-Date:2021-01-06 14:06:18
Revision:17444
Is-Local-Build:true

Identification: JOSM/1.5 (17444 SVN en) Windows 10 64-Bit
OS Build number: Windows 10 Home 2004 (19041)
Memory Usage: 719 MB / 1820 MB (374 MB allocated, but free)
Java version: 1.8.0_272-b10, AdoptOpenJDK, OpenJDK 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1920×1080 (scaling 1.00×1.00)
Maximum Screen Size: 1920×1080
Best cursor sizes: 16×16→32×32, 32×32→32×32
VM arguments: [-agentlib:jdwp=transport=dt_socket,suspend=y,address=localhost:55510, -ea, -Djosm.homexxx=c:\temp\josmxxx, -javaagent:D:\eclipse-java-2020-09\eclipse\configuration\org.eclipse.osgi\215\0\.cp\lib\javaagent-shaded.jar, -Dfile.encoding=UTF-8]

Plugins:
+ ColumbusCSV (35640)
+ OpeningHoursEditor (35640)
+ apache-commons (35524)
+ buildings_tools (35669)
+ ejml (35458)
+ geotools (35458)
+ jaxb (35543)
+ jts (35458)
+ o5m (35640)
+ opendata (35640)
+ pbf (35650)
+ poly (35640)
+ reverter (35640)
+ undelete (35640)
+ utilsplugin2 (35674)

Validator rules:
+ c:\josm\core\resources\data\validator\geometry.mapcss

[GerdP]

If it is too difficult to detect this case it might be good to implement #18065