All islands [landuse=*] inside [natural=water] mapped as multipolygon are considered as ERROR by JOSM validation: 'Coastline inside natural=water'

[AnkEric]

What steps will reproduce the problem?

JOSM Validation on:
multipolygon ("water"): 2-members
outer way = [natural=water]
inner way = [landuse=*] (which is an "island")

JOSM validation:
Error: "Coastline inside natural=water"

Error is new to JOSM v.12542.

What is the expected result?

This is no Error.
IMO: multipolygon is correct.
Or: ALL islands have been mapped incorrectly (meaning thousands).

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2017-07-30 17:07:42 +0200 (Sun, 30 Jul 2017)
Build-Date:2017-07-30 15:14:00
Revision:12542
Relative:URL: ^/trunk

Identification: JOSM/1.5 (12542 en) Windows 10 64-Bit
OS Build number: Windows 10 Home 1703 (15063)
Memory Usage: 531 MB / 910 MB (235 MB allocated, but free)
Java version: 1.8.0_141-b15, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: \Display0 1920x1080
Maximum Screen Size: 1920x1080
Dataset consistency test: No problems found

Plugins:
+ Mapillary (v1.5.5)
+ OpeningHoursEditor (33185)
+ apache-commons (32994)
+ apache-http (32699)
+ contourmerge (1030)
+ reverter (33088)
+ routes (33292)
+ turnrestrictions (33088)
+ utilsplugin2 (33328)

Tagging presets:
+ <josm.pref>\presets\NL_fiets_preset.xml
+ <josm.pref>\presets\Picnic_table.xml

Last errors/warnings:
- E: Failed to locate image 'presets/bike.png'
- W:  Fietspaden: Could not get presets icon presets/bike.png
- W: java.net.SocketTimeoutException: Read timed out

[Klumbumbus]

Closed as duplicate of #15108.