With Preview Data option enabled....

1) With open dirty editor (requires save)
2) Close it's project
3) Requires Save Dialog is presented, choose OK
4) Error stack trace below...

org.eclipse.core.internal.resources.ResourceException: Resource '/SimpleDatatypesTest' is not open.
at org.eclipse.core.internal.resources.Project.checkAccessible(Project.java:137)
at org.eclipse.core.internal.resources.File.create(File.java:123)
at org.eclipse.core.internal.resources.File.create(File.java:196)
at org.teiid.designer.runtime.preview.jobs.CreatePreviewVdbJob.runImpl(CreatePreviewVdbJob.java:126)
at org.teiid.designer.runtime.preview.jobs.WorkspacePreviewVdbJob.runInWorkspace(WorkspacePreviewVdbJob.java:126)
at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:38)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)

Guessing the close project thread is completing before the CreatePreviewVdbJob gets to check it's project status.