java: javacTask: source release 8 requires target release 1.8 (sbt project)

I have an sbt project:

name := "experiments"

scalaVersion := "2.10.4"

javacOptions ++= Seq("-source", "1.8","-target","1.8")

version := "1.0"

This imports ok and I can see in the java compiler settings , Project Bytecode level is 1.8 and additional compiler parameters are -source 1.8 -target 1.8

But still when I compile the project, I get this error:

java: javacTask: source release 8 requires target release 1.8 (sbt project)

Any ideas what might be wrong?