Fixed accessibility labels are not always created in problems.

STUD-1524

common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee

@@ -538,7 +538,7 @@ describe 'MarkdownEditingDescriptor', ->
     
     <p>What is the capital of Germany?</p>
     <multiplechoiceresponse>
-      <choicegroup type="MultipleChoice">
+      <choicegroup label="What is the capital of Germany?" type="MultipleChoice">
         <choice correct="false">Bonn</choice>
         <choice correct="false">Hamburg</choice>
         <choice correct="true">Berlin</choice>

common/lib/xmodule/xmodule/js/src/problem/edit.coffee

@@ -359,7 +359,7 @@ class @MarkdownEditingDescriptor extends XModule.Descriptor
       // looks for >>arbitrary text<< and inserts it into the label attribute of the input type directly below the text. 
       var split = xml.split('\n');
       var new_xml = [];
-      var line, i, curlabel = '';
+      var line, i, curlabel, prevlabel = '';
       var didinput = false;
       for (i = 0; i < split.length; i++) {
         line = split[i];
@@ -370,13 +370,14 @@ class @MarkdownEditingDescriptor extends XModule.Descriptor
             .replace(/"/g, '&quot;')
             .replace(/'/g, '&apos;');
           line = line.replace(/>>|<</g, '');
-        } else if (line.match(/<\w+response/) && didinput) {
+        } else if (line.match(/<\w+response/) && didinput && curlabel == prevlabel) {
           // reset label to prevent gobbling up previous one (if multiple questions)
           curlabel = '';
           didinput = false;
-        } else if (line.match(/<(textline|optioninput|formulaequationinput|choicegroup|checkboxgroup)/) && curlabel != '') {
+        } else if (line.match(/<(textline|optioninput|formulaequationinput|choicegroup|checkboxgroup)/) && curlabel != '' && curlabel != undefined) {
           line = line.replace(/<(textline|optioninput|formulaequationinput|choicegroup|checkboxgroup)/, '<$1 label="' + curlabel + '"');
           didinput = true;
+          prevlabel = curlabel;
         }
         new_xml.push(line);
       }