Problem with acrobat 9 when validating text fields

Question

Hello
I've been using a script to provide feedback for my English Students. The correct input turns the backgroundcolor to green, an incorrect one turns it to red. This script has been working fine for many years including Acrobat Reader 8, but version 9 gives me a problem. When filling in the field and pressing enter, nothing happens, only when you give focus to the filled in field again does the color change. Leaving the field turns the color again to its original. Here is a link to an example:
http://schulen.eduhi.at/herderschule/pdf/E3/e3u1sentences.pdf
Try it with reader 9 and a previous version and you'll see what I mean.
Can somebody help me fix this problem?
Here is the code that I'm using to validate the textfields:
//TestLetter
/*********** belongs to: Document-Level:TestLetter ***********/
     var f = this.getField("1")
          f.value = "";
     var f = this.getField("2")
          f.value = "";       
function TestLetter(FieldName,FieldValue)
  var RetValue;
   RetValue = false;
  switch (FieldName)
    case "1":
      if (FieldValue == "in the Australian bush.")
           RetValue = true;
         break;
    case "2":
      if (FieldValue == "for a pack of dingoes.")
           RetValue = true;
             break;
     default:
     RetValue = false;
     break;
  return  RetValue;
//trim
/*********** belongs to: Document-Level:trim ***********/
function trim(inputString) {
   if (typeof inputString != "string") { return inputString; }
   var retValue = inputString;
   var ch = retValue.substring(0, 1);
   while (ch == " ") {
      retValue = retValue.substring(1, retValue.length);
      ch = retValue.substring(0, 1);
   ch = retValue.substring(retValue.length-1, retValue.length);
   while (ch == " ") {
      retValue = retValue.substring(0, retValue.length-1);
      ch = retValue.substring(retValue.length-1, retValue.length);
   while (retValue.indexOf("  ") != -1) {
      retValue = retValue.substring(0, retValue.indexOf("  "))
    + retValue.substring(retValue.indexOf("  ")+1, retValue.length);
   return retValue;
//1:Validate
/*********** belongs to: AcroForm:1:Validate ***********/
event.value = trim(event.value);
var f = this.getField("1"); /* field that the event occurs at */
     f.readonly = false;
     f.fillColor = color.ltGray
if (event.value != "")
  if (TestLetter("1",event.value)==true)
    f.fillColor = color.green;
else
  f.fillColor = color.red;
//2:Validate
/*********** belongs to: AcroForm:2:Validate ***********/
event.value = trim(event.value);
var f = this.getField("2"); /* field that the event occurs at */
     f.readonly = false;
     f.fillColor = color.ltGray
if (event.value != "")
  if (TestLetter("2",event.value)==true)
    f.fillColor = color.green;
Else
f.fillColor = color.red;

Answer 1

You probably have field highlighting turned on. You can use JavaScript in the file to turn off this user preference setting.
I'd also suggest a code change:
event.value = trim(event.value);
var f = event.target; /* field that the event occurs at */
George