I think this issue is general for enums (i.e. not only enums with custom labels).

Looking at MoBIE's OpenCollectionTableCommand.DataRoot:
https://github.com/mobie/mobie-viewer-fiji/blob/18700b576efcc9574a9395598939bbf354f970e7/src/main/java/org/embl/mobie/command/open/OpenCollectionTableCommand.java#L49-L53

... non-default values seem to be correctly persisted to preference storage:

#@ PrefService ps
#@ ConvertService cs

import org.embl.mobie.command.open.OpenCollectionTableCommand
import org.embl.mobie.command.open.OpenCollectionTableCommand.DataRoot

stringValue = ps.get(OpenCollectionTableCommand.class, "dataRoot")

println(stringValue)  // e.g. UseTableFolder

converted = cs.convert(stringValue, DataRoot.class)

println(converted)  // e.g. UseTableFolder
println(converted.class)  // class org.embl.mobie.command.open.OpenCollectionTableCommand$DataRoot

However, the command dialog still falls back to default value every time.

Hence I think the issue is somewhere in the command module processing, not in the preferences.

@ctrueden would you have a best guess where to dig next?

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/scijava-persist-not-working-for-enums/99827/7

I noticed that persisted enum values are actually harvested just fine: as long as you don't touch the dropdown widget, the persisted value is kept. It's just the UI that isn't updated to reflect the persisted value 🤦

Consider this Groovy script:

#@ org.scijava.ItemIO itemio

println itemio

When you run it, the dialog will always show the first enum value, INPUT:

However, if you choose an alternative value (e.g. BOTH), press OK, and re-run the script, this time without changing in the dropdown (that again shows INPUT), the correct, persisted value (i.e. BOTH) will be printed.

That means this issue actually belongs to scijava-ui-swing 🚀 .

(NB: This didn't work in older Fiji installation of mine that had scijava-common-2.94.2, so the persisting behavior must have changed between that version and scijava-common-2.99.0)

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/scijava-persist-not-working-for-enums/99827/9

Hi @imagejan and @ctrueden, are those changes already shipped with Fiji? I think I observed some strange behaviour related to the persistence of enums. I would investigate more if you tell me that those changes are already in place.

I am sorry 😬 !

I did not carefully read @imagejan's above post.
In fact it seems that he exactly found what I found.
I also saw now that the PR has not been merged yet.

tl;dr please simply ignore all my comments.