relativizeLibs is ignored?

How is one supposed to use relativizeLibs? It won't work as an additional argument to eclipse:

> eclipse relativizeLibs=false
[error] Expected whitespace character
[error] Expected 'execution-environment'
[error] Expected 'skip-parents'
[error] Expected 'with-source'
[error] Expected 'with-javadoc'
[error] Expected 'with-bundled-scala-containers'
[error] eclipse relativizeLibs=false
[error]         ^

If I set it explicitly, it is ignored too:

> set EclipseKeys.relativizeLibs := false
[info] Defining spark/*:eclipseRelativizeLibs
[info] The new value will be used by no settings or tasks.
[info] Reapplying settings...
[info] Set current project to spark-parent (in build file:/Volumes/Thunderbolt_SSD/dragos/workspace/Spark/dev/spark/)

(I checked the contents of .classpath)

However, if I first change the project, it is taken into account (for that project):

> project core
[info] Set current project to spark-core (in build file:/Volumes/Thunderbolt_SSD/dragos/workspace/Spark/dev/spark/)
> set EclipseKeys.relativizeLibs := false
[info] Defining core/*:eclipseRelativizeLibs
[info] The new value will be used by no settings or tasks.
[info] Reapplying settings...
[info] Set current project to spark-core (in build file:/Volumes/Thunderbolt_SSD/dragos/workspace/Spark/dev/spark/)
> eclipse with-source=true

Reproduce the reported commands with the eclipse task, relativizeLibs=false, and EclipseKeys.relativizeLibs := false, then inspect how the current project and spark/* settings are selected. Done means the setting is accepted in the intended context and changes the generated .classpath as expected.