Xbase/Xtend and Undo Jdt save actions dont like each other

https://user-images.githubusercontent.com/238736/137960220-3b226d46-73bc-422e-b355-c50e4a3520e4.mov

java.lang.IllegalStateException: Could not create binding for 'lala.Viech' in context of project 'lala'.
	at org.eclipse.xtext.common.types.access.jdt.JdtBasedTypeFactory.createType(JdtBasedTypeFactory.java:338)
	at org.eclipse.xtext.common.types.access.jdt.JdtBasedTypeFactory.createType(JdtBasedTypeFactory.java:415)
	at org.eclipse.xtext.common.types.access.jdt.JdtBasedTypeFactory.createType(JdtBasedTypeFactory.java:1)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeMirror.initialize(JdtTypeMirror.java:68)
	at org.eclipse.xtext.common.types.access.TypeResource.doLoad(TypeResource.java:135)
	at org.eclipse.emf.ecore.resource.impl.ResourceImpl.load(ResourceImpl.java:1563)
	at org.eclipse.xtext.common.types.access.TypeResource.load(TypeResource.java:121)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.createResourceAndFindType(JdtTypeProvider.java:290)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.findObjectTypeInJavaProject(JdtTypeProvider.java:273)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.doFindObjectType(JdtTypeProvider.java:216)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.findObjectType(JdtTypeProvider.java:196)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.doFindTypeByName(JdtTypeProvider.java:154)
	at org.eclipse.xtext.common.types.access.jdt.JdtTypeProvider.findTypeByName(JdtTypeProvider.java:163)
	at org.eclipse.xtext.common.types.xtext.AbstractTypeScope.getSingleElement(AbstractTypeScope.java:60)
	at org.eclipse.xtext.common.types.xtext.AbstractTypeScope.getSingleElement(AbstractTypeScope.java:55)
	at org.eclipse.xtend.core.scoping.LocalResourceFilteringTypeScope.getSingleElement(LocalResourceFilteringTypeScope.java:43)
	at org.eclipse.xtend.core.scoping.RecordingTypeScope.getSingleElement(RecordingTypeScope.java:52)
	at org.eclipse.xtend.core.scoping.TypeScopeWithWildcardImports.getSingleElementFromParent(TypeScopeWithWildcardImports.java:73)
	at org.eclipse.xtend.core.scoping.TypeScopeWithWildcardImports.getSingleElement(TypeScopeWithWildcardImports.java:67)
	at org.eclipse.xtend.core.scoping.AbstractKnownTypesScope.getSingleElement(AbstractKnownTypesScope.java:43)
	at org.eclipse.xtend.core.scoping.PrimitiveAwareScope.getSingleElement(PrimitiveAwareScope.java:40)
	at org.eclipse.xtend.core.scoping.CachingTypeScope.getSingleElement(CachingTypeScope.java:41)
	at org.eclipse.xtend.core.scoping.AbstractKnownTypesScope.getSingleElement(AbstractKnownTypesScope.java:43)
	at org.eclipse.xtext.linking.impl.DefaultLinkingService.getLinkedObjects(DefaultLinkingService.java:115)
	at org.eclipse.xtext.linking.lazy.LazyLinkingResource.getEObject(LazyLinkingResource.java:266)
	at org.eclipse.xtext.xbase.resource.BatchLinkableResource.getEObject(BatchLinkableResource.java:120)
	at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.getEObject(ResourceSetImpl.java:223)
	at org.eclipse.emf.ecore.util.EcoreUtil.resolve(EcoreUtil.java:209)
	at org.eclipse.emf.ecore.util.EcoreUtil.resolve(EcoreUtil.java:269)

undoing a save action that organizes imports leads to failing JdtBasedTypeProvider
=> Xtend file may get broken.

upon fixing the java file, the xtend file wont be built again
e.g. cause
JdtQueuedBuildData.doNeedRebuild(JavaBuilderState, Procedure1<? super UnconfirmedStructuralChangesDelta>)
says no (same last built date, am not sure if this is the correct place that should trigger affection)

Reproduce the failure by undoing a save action that organizes imports, then inspect JdtBasedTypeProvider and JdtQueuedBuildData, both identified in the report and stack trace. Trace why the Xtend file is not rebuilt after the Java file is fixed; done means the undo scenario no longer breaks the Xtend file and a subsequent Java change triggers its rebuild.