https://bugzilla.redhat.com/show_bug.cgi?id=1263580
--- Comment #9 from Mat Booth mat.booth@redhat.com --- Aha, so the problem is because I did not get the maven-indexer update at the same time as the eclipse-m2e-core update.
As discussed on IRC, amending the Requires on maven-indexer should fix this -- thanks for your help!