On MacOS the JNLP parameter "java-vm-args" terminate the Java Web Start directly. A workaround is to use "initial-heap-size" and "max-heap-size". See the attached jnlp samples.

 

java version "1.7.0_08-ea"

Java(TM) SE Runtime Environment (build 1.7.0_08-ea-b04)

Java HotSpot(TM) 64-Bit Server VM (build 23.4-b01, mixed mode)