Given is a 64-bit Windows box, where both 64-bit Java SE 7 Update 9 and
32-bit Java SE 6 Update 37 are installed.
Furthermore, there is a Java Web Start application that requires to run on Java SE 6.
This requirement is explicitly given in the jnlp file:
% grep j2se jacc.jnlp
<j2se version="1.6" max-heap-size="512m"/>
The following behaviour is strictly reproducible:
Java Web Start of JRE 7 is used, if this JRE 7 was installed most recently.
Java Web Start of JRE 6 is used, if this JRE 6 was installed most recently.
The behaviour was introduced with Java SE 7 Update 6.
Java SE 7 Update 5 was still fine in this respect:
regardless of the installation order, Java Web Start of JRE 1.6.0 was used.