When trying to define a filter with as a search option a chekbox field, I got the error messages:

Warrning: array_merge() [function.array-merge]: Argument #2 is not an array in /[...]/mod/dataform/field/multiselect/renderer.php on line 191

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /[...]/mod/dataform/filter/filter_form.php on line 186

and

Notice: Undefined variable: type in [...]/lib/pear/HTML/QuickForm/group.php on line 277

This problem does not happen with a radio button field.