OPERATING SYSTEM(S):
Linux ( and probably all Unix based JDKs )

FULL JDK VERSION(S):
java full version "1.5.0_06-b05"

DESCRIPTION:
The following testcase illustrates the problem.
ProcessTest.java
public class ProcessTest {
    public static void main(String argv[]) {
        try {
            Process p = Runtime.getRuntime().exec("java Test");
            p.waitFor();
            System.out.println("exit = " + p.exitValue());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
Test.java
public class Test
{
  public static void main(String args[])
  {
    System.exit(-10);
  }
}

On Windows one gets
java ProcessTest
exit = -10

On Linux one gets
java ProcessTest
exit = 246

This can be a problem on Unix if the WEXITSTATUS macro is not cast to a signed char before assigning to the return value.