EDIT

now the Unit ID mapping is a combo box and the dna provider is a combo box containing the providers defined in the preferences as well.

Trying to create a new provider results in

login : admin
editor version : 5.10.0.201909180750
server : localhost (localhost mgd.)
schema version : 5.8.2.0.20190815
os : Windows Server 2012 R2 6.3 amd64
java : 1.8.0_121
java.lang.IllegalArgumentException: Index out of bounds
    at org.eclipse.swt.SWT.error(SWT.java:4514)
    at org.eclipse.swt.SWT.error(SWT.java:4448)
    at org.eclipse.swt.SWT.error(SWT.java:4419)
    at org.eclipse.swt.widgets.Widget.error(Widget.java:482)
    at org.eclipse.swt.widgets.List.add(List.java:150)
    at eu.etaxonomy.taxeditor.preference.ListComponent$AddListener.mouseUp(ListComponent.java:293)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:221)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4418)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4236)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3824)
    at org.eclipse.jface.window.Window.runEventLoop(Window.java:818)
    at org.eclipse.jface.window.Window.open(Window.java:794)
    at eu.etaxonomy.taxeditor.workbench.handler.OpenAdminPreferencesHandler.execute(OpenAdminPreferencesHandler.java:125)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:282)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:264)
    at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
    at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:152)
    at org.eclipse.core.commands.Command.executeWithChecks(Command.java:494)
    at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:488)
    at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:210)
    at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.executeItem(HandledContributionItem.java:433)
    at org.eclipse.e4.ui.workbench.renderers.swt.AbstractContributionItem.handleWidgetSelection(AbstractContributionItem.java:454)
    at org.eclipse.e4.ui.workbench.renderers.swt.AbstractContributionItem$3.handleEvent(AbstractContributionItem.java:482)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4418)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4236)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3824)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:693)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:610)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
    at eu.etaxonomy.taxeditor.Application.start(Application.java:24)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)

Second time it worked but still there was an empty entry in the provider list

The "New provider" text field should have a label "New provider" or similar. Also the "Add Provider" button should be placed behind the text field to make clear that the text in the "New provider" textfield will be added to the list.

This is fixed but still "Restore default" does not completely remove the preference (and even does not clear the existing list, what I would expect)

This to me also does not seem to be fixed yet. Did you push your ABCD preference changes?

Andreas Müller wrote:

This is fixed but still "Restore default" does not completely remove the preference (and even does not clear the existing list, what I would expect)

This to me also does not seem to be fixed yet. Did you push your ABCD preference changes?

maybe jenkins did not build, I started the job now.