Multiselect presets doesn't work properly

[gaben]

What steps will reproduce the problem?

1. Add a node with a combo choice in the presets (eg. amenity=restaurant)
2. Open preset editor, select at least two items, apply
3. Reopen the preset

What is the expected result?

The selection remains on the items, no override possible.

What happens instead?

Next time you open the preset, anything you click on will override existing tags, so data loss is possible.

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

Plugins not affecting this, reproducible on both Win and Linux.
If an object has only a single value, the whole list is greyed out and not modifiable by the preset.

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2020-09-17 21:42:16 +0200 (Thu, 17 Sep 2020)
Build-Date:2020-09-18 01:30:49
Revision:17036
Relative:URL: ^/trunk

Identification: JOSM/1.5 (17036 hu) Windows 10 64-Bit
OS Build number: Windows 10 Pro for Workstations 2004 (19041)
Memory Usage: 813 MB / 1820 MB (346 MB allocated, but free)
Java version: 1.8.0_261-b12, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1920x1200 (scaling 1.0x1.0)
Maximum Screen Size: 1920x1200
Best cursor sizes: 16x16 -> 32x32, 32x32 -> 32x32
VM arguments: [-Djava.security.manager, -Djava.security.policy=file:<java.home>\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.home=<java.home>\bin, -Djnlpx.origFilenameArg=%UserProfile%\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\31\583aa85f-56e18fc1, -Djnlpx.remove=false, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlpx.heapsize=NULL,2048m, -Djnlpx.splashport=55776, -Djnlp.application.href=https://josm.openstreetmap.de/download/josm-latest.jnlp, -Djnlpx.jvm=<java.home>\bin\javaw.exe]
Dataset consistency test: No problems found

[Don-vip]

Replying to Klumbumbus:

You added the regression keyword, do you know the last version for which it worked?

[Klumbumbus]

No, I was just pretty sure that it worked in the past.
BTW: welcome back :)

[Don-vip]

Replying to Klumbumbus:

BTW: welcome back :)

Thanks! I'm glad to see all of you have continued to work on JOSM during my absence :) I need to catch up with everything you did :) Nice icons!

[Klumbumbus]

r16686 works, r16703 doesn't work. So regression is here: https://josm.openstreetmap.de/log/josm/?rev=16703&stop_rev=16687&limit=900

[gaben]

Fun fact, just hours before your comment checked where are you or why you left :) Welcome back.

[Don-vip]

In 17077/josm:

fix #19813 - see #16031 - fix selection of Multiselect presets (regression from r16687:16688)