JOSM displays line which doesn't exist in the data

[anonymous]

What steps will reproduce the problem?

1. Open attached file y.osm
2. Run Validator, this should find 23 errors
3. Open the error list
4. Open the "unordered coastline" list
5. Right click the first error (id 4.556.782), choose "Zoom to problem"
6. Press - (Minus) three times to zoom out

What is the expected result?

A view of a part of the coastline

What happens instead?

The coastline is displayed, but also a blue line going to nowhere. This line disappears
when you try to zoom in on it.

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: 2016-07-11 23:04:49 +0200 (Mon, 11 Jul 2016)
Build-Date:2016-07-12 01:31:48
Revision:10526
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10526 en) Windows 10 64-Bit
Memory Usage: 5711 MB / 5711 MB (4360 MB allocated, but free)
Java version: 1.8.0_102-b14, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
VM arguments: [-Dsun.java2d.opengl=true]
Dataset consistency test: No problems found

Plugins:
- FastDraw (32639)
- apache-commons (32584)
- buildings_tools (32639)
- ejml (32639)
- geotools (32584)
- jts (32539)
- o5m (UNKNOWN)
- opendata (32584)
- pbf (32584)
- poly (32584)
- reverter (32584)
- utilsplugin2 (32584)

Last errors/warnings:
- W: Unable to delete file <josm.cache>\tiles\TMS.key
- W: Unable to delete file <josm.cache>\tiles\TMS.data
- W: Unable to delete file <josm.cache>\tiles\TMS_BLOCK.key
- W: Unable to delete file <josm.cache>\tiles\TMS_BLOCK.data
- W: Unable to delete file <josm.cache>\tiles\TMS_INDEX.key
- W: Unable to delete file <josm.cache>\tiles\TMS_INDEX.data
- W: Unable to delete file <josm.cache>\tiles\TMS_INDEX_v2.key
- W: Unable to delete file <josm.cache>\tiles\TMS_INDEX_v2.data

[GerdP]

Forgot to enter my email address, done now.

[Klumbumbus]

Closed as duplicate of #8429.
This is a rendering artefact of line casing. Known but unresolved.