This

public class test 
{
    public static void main(String[] args) 
    {
        Object o = null;
        assert o != null;
        if(o != null)
          System.out.println("o != null");
    }
}

prints out "o != null"; both 1.5_22 and 1.6_18. Compiler bug? Commenting out the assert fixes it. The byte code appears to jump directly to the print statement when assertions are disabled:

 public static main(String[]) : void
   L0
    LINENUMBER 5 L0
    ACONST_NULL
    ASTORE 1
   L1
    LINENUMBER 6 L1
    GETSTATIC test.$assertionsDisabled : boolean
    IFNE L2
    ALOAD 1: o
    IFNONNULL L2
    NEW AssertionError
    DUP
    INVOKESPECIAL AssertionError.<init>() : void
    ATHROW
   L2
    LINENUMBER 8 L2
    GETSTATIC System.out : PrintStream
    LDC "o != null"
    INVOKEVIRTUAL PrintStream.println(String) : void
   L3
    LINENUMBER 9 L3
    RETURN
   L4