Display problem for riverbank multipolygon

[skorbut]

What steps will reproduce the problem?

1. Download the bounding box 47.3401576,9.1186118,47.3481306,9.1361138 using JOSM -> Download Icon -> Tab: Bounding Box ​https://www.openstreetmap.org/#map=18/47.346514/9.127867
2. Make sure the downloaded area contains the hamlets "Husen" and "Adelbach"

What is the expected result?

JOSM should display the data fine.

What happens instead?

There seems to be some kind of display artifact (a blue line going from NNW to SSE), probably induced by the partially downloaded riverbank multipolygon. The artifact is only visible in the default view right after the download and when zooming in, i.e. the artifact is not visible wheen zooming out. The artifact reappears after zooming in again. See screenshots.

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

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-08-05 13:43:42 +0200 (Thu, 05 Aug 2021)
Revision:18125
Build-Date:2021-08-05 11:54:28
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (18125 en) Linux Ubuntu 18.04.5 LTS
Memory Usage: 788 MB / 7976 MB (424 MB allocated, but free)
Java version: 11.0.11+9-Ubuntu-0ubuntu2.18.04, Ubuntu, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.metal.MetalLookAndFeel
Screen: :0.0 1920×1080 (scaling 1.00×1.00)
Maximum Screen Size: 1920×1080
Best cursor sizes: 16×16→16×16, 32×32→32×32
Environment variable LANG: en_US.UTF-8
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_US
Numbers with default locale: 1234567890 -> 1234567890
Desktop environment: MATE
Java package: openjdk-11-jre:amd64-11.0.11+9-0ubuntu2~18.04
Java ATK Wrapper package: libatk-wrapper-java:all-0.33.3-20ubuntu0.1
libcommons-logging-java: libcommons-logging-java:all-1.2-2
fonts-noto: fonts-noto:all-20171026-2
VM arguments: [--add-modules=java.scripting,java.sql, -Djosm.restart=true, -Djosm.dir.name=JOSM-latest, -Djava.net.useSystemProxies=true]
Dataset consistency test: No problems found

Plugins:
+ Mapillary (2.0.0-alpha.30-dirty)
+ apache-commons (35524)
+ apache-http (35589)
+ jna (35662)