In my opinion, since the questions are in same group we enter a code branch where the textarea wants the group conditions checked under onkeyup=""
The presentation being question-by-question causes some javascript to be lacking, because the group logic is not useful during question-by-question

hence the textarea wants the checks, the survey doesn't give the checks implementations.

here is the patch I coded, that is simply adding the definition of noop_checkconditions() in one ELSE branch. The IF branch was already setup to implement it
(Well, it's a void function, but IE still need the implementation for not throwing that Expected object nag)

--- question.php.orig 2010-02-08 14:49:51.000000000 +0100
+++ question.php 2010-02-08 14:51:20.000000000 +0100
@@ -472,6 +472,9 @@
echo "\n\n<!-- JAVASCRIPT FOR CONDITIONAL QUESTIONS -->\n";
echo "\t<script type='text/javascript'>\n";
echo "\t<!--\n";

• echo "function noop_checkconditions(value, name, type)\n";
• echo "\t{\n";
• echo "\t}\n";
  echo "function checkconditions(value, name, type)\n";
  echo "\t{\n";
  echo "\t}\n";