Existence of 'restriction' relations makes zooming/panning unbearably slow

[Skybunny]

What steps will reproduce the problem?

1. Download this in the Overpass API:

(type:way and ref:CTH) in "Marathon County, Wisconsin"

2. Search for the following:

type:way

3. 'Download parent ways and relations' of the ~560 ways you'll get.

What is the expected result?

Zooming in and out should be smooth/quick.

What happens instead?

If (and only if) the restrictions that will be downloaded here are "in scope", meaning they have not been filtered in the relations search box, zooming/panning is very very slow/poor performance. The following searches in the Relations window will prove this out:

'County Highway': zooming in and out is fast; no relations are in the filter at all.
'restriction': zooming is 'very' slow.
NULL (no search term): zooming is 'very' slow.
'no_u_turn' (only two hits returned): zooming is pretty fast.
'no_left_turn' (40 hits returned): zooming is slow.

Purging the restriction relations will have the same basic effect. Suddenly, zooming/rendering performance improves.

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

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2018-09-23 15:17:18 +0200 (Sun, 23 Sep 2018)
Revision:14271
Build-Date:2018-09-24 01:32:44
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (14271 en) Mac OS X 10.14
OS Build number: Mac OS X 10.14 (18A389)
Memory Usage: 411 MB / 5120 MB (232 MB allocated, but free)
Java version: 10.0.2+13, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: Display 69680128 1440x900
Maximum Screen Size: 1440x900
Dataset consistency test: No problems found

Plugins:
+ FastDraw (34510)
+ apache-commons (34506)
+ ejml (34389)
+ geojson (87)
+ geotools (34513)
+ jts (34524)
+ opendata (34662)
+ pbf (34576)
+ utilsplugin2 (34506)

Last errors/warnings:
- W: No configuration settings found.  Using hardcoded default values for all pools.
- W: java.net.SocketException: Socket closed
- E: java.net.SocketException: Socket closed