"Path for project must have only one segment" when EAR project set is in a subdirectory

It appears that if I group the project directories for an EAR-style Seam project under a subdirectory of my workspace, Eclipse gives the error below.

So, my workspace is C:\proj

I generated a new Seam 2.0 project, creating:

C:\proj\newproj
C:\proj\newproj-ear
C:\proj\newproj-ejb
C:\proj\newproj-test

I then put them in another dir (I've got a lot of projects):

C:\proj\newproj\newproj
C:\proj\newproj\newproj-ear
C:\proj\newproj\newproj-ejb
C:\proj\newproj\newproj-test

Then I imported them and got the error that follows. Note however that the code/debug cycle and deployment to the application server does work. Presumably the impact occurs at time of packing (unconfirmed).

Putting the project back into C:\proj resolves this issue, however importing from other directories without copying the files into the workspace is a pretty common way to work AFAIK.

Warning
Mon Nov 19 14:05:50 MST 2007
Path for project must have only one segment.

java.lang.IllegalArgumentException: Path for project must have only one segment.
at org.eclipse.core.runtime.Assert.isLegal(Assert.java:62)
at org.eclipse.core.internal.resources.WorkspaceRoot.getProject(WorkspaceRoot.java:165)
at org.jboss.ide.eclipse.archives.core.model.other.internal.WorkspacePreferenceManager.getResource(WorkspacePreferenceManager.java:54)
at org.jboss.ide.eclipse.archives.core.model.other.internal.WorkspacePreferenceManager.isBuilderEnabled(WorkspacePreferenceManager.java:62)
at org.jboss.ide.eclipse.archives.core.project.ArchivesBuilder.build(ArchivesBuilder.java:66)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:624)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:166)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:197)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:246)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:249)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:302)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:334)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:137)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:235)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)