If entered few category name in parameter "category", like '{cms_module
module=Questions category="category1,categoey2,category3"}', then module is not
displayed.

I solved this problem like this:
in file module - /modules/Questions/function.default_summary.php
replace strings in position 34
  $categories = '';
  if( isset($params['category']) && $params['category'] != '' ){
    $categories = str_replace("'",'_',$params['category']);
  }
to
  $categories = '';
  if( isset($params['category']) && $params['category'] != '' ){
    $categories = str_replace("'",'_',$params['category']);
    $categories = preg_replace("|,|","','",$categories);
  }