Executing this command line with JDK 8u40 b03 (or JDK 7):

$ java -XX:-UseParallelGC -version

will start the JVM with the SerialGC. Using the same command line in JDK 8u40 b09 will start with ParallelGC:

$ /java -XX:+PrintFlagsFinal -XX:-UseParallelGC -version | grep UseParallelGC
     bool UseParallelGC := true {product}
java version "1.8.0_40-ea"
Java(TM) SE Runtime Environment (build 1.8.0_40-ea-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b13, mixed mode)

While I think it is a bit odd to only say which GC you don't want I'm guessing that this is probably not an intended change.