Tested using FX Cont trunk build 370 with SDK:
Product: javafx-1.0dev, Platform: windows-i586, Build-Number: 742, Build-ID: 2008-10-14_19-32-24 on NB6.5: 
Product Version: NetBeans IDE Dev (Build 200810130704)
Java: 1.6.0_10-rc; Java HotSpot(TM) Client VM 11.0-b14
System: Windows Vista version 6.0 running on x86; Cp1252; en_US (nb)

If you have indented javadoc comments and press enter, it always puts the ' *'.

1. paste
/**
 * A Simple Test It Class
 * @author Lark
 */
public class NewJavaFXEmpty {
    /** First Name */
    var firstName : String = "Test";

    /** Last Name */
    var age : Number = 39;

    /** 
     * A Foo Function
     * @param   a   A simple string
     * @return      A test String
     */
    function Foo (a:String):String {
        return "test"
    }
}

2. Go to javadoc before Foo and press enter at any point.  You end up with ' *' instead of matching indents for '*'