I'm using Juno 4.2 with latest spring, maven plugin and JDK1.6.0_25.
I faced same issue and here is my fix that make default after each Eclipse restart:
- List item
- Right-click on the maven project
- Java Build Path
- Libraries tab
- Select current wrong JRE item
- Click Edit
- Select the last option (Workspace default JRE (jdk1.6.0_25)