Resolving member conflicts in relation shows member details only for one side of conflict

[Dakon]

What steps will reproduce the problem?

1. Try to resolve a member conflict in a partially downloaded relation.
2. Cancel, download the incomplete members of that relation.
3. Try to resolve the conflict again.

What is the expected result?

Both sides in the conflict editor show the details about the (common) members of the relation.

What happens instead?

Only the left side shows the defails of the members, the right side shows "incomplete" for most of them. If I hover them I see the id, and for almost all of them it's exactly the same as on the left side. In my case there is actually one member where the details are shown on the right side. This member has nothing special I can identify.

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: 2016-03-13 01:17:21 +0100 (Sun, 13 Mar 2016)
Build-Date:2016-03-13 02:35:00
Revision:9979
Relative:URL: ^/trunk

Identification: JOSM/1.5 (9979 de) Linux openSUSE 13.1 (Bottle) (x86_64)
Memory Usage: 341 MB / 910 MB (166 MB allocated, but free)
Java version: 1.7.0_99-b00, Oracle Corporation, OpenJDK 64-Bit Server VM
Java package: java-1_7_0-openjdk:x86_64-1.7.0.99
Dataset consistency test: No problems found

Plugins:
- FixAddresses (31772)
- OpeningHoursEditor (31772)
- buildings_tools (31895)
- geochat (31895)
- imagery_offset_db (32046)
- jna (31877)
- native_password_manager (31772)
- osmarender (31772)
- pbf (32128)
- poly (31772)
- public_transport (31895)
- reverter (32005)
- terracer (31895)
- turnrestrictions (31895)
- undelete (31895)
- utilsplugin2 (32099)

Last errors/warnings:
- W: Hinzufügen von resource://data/validator/power.mapcss zu Eigenschaftsprüfer fehlgeschlagen
- W: java.io.IOException: Das Öffnen eines Eingabestroms für die Resource 'resource://data/validator/power.mapcss' ist fehlgeschlagen.

[Dakon]

screenshot of conflict resolution

[skyper]

See #14094 for a similar problem with the property tab.