Limit values to result set - no result with special characters in selective filter

Hi,
I have two exposed filters, one for taxonomy terms (selective) and second one for selecting vocabulary. I want to limit the values to result set, but it stops work, when the taxonomy contain special characters - this values are not shown in select form. It is probably due to that the select list value contains non safety values. For example:

  <option value="Zimn%C3%AD+%C3%BAdr%C5%BEba">Zimní údržba</option>

(This option value is created when the Limit values to result set is not checked, after enabling that function this value disappear).
Example of non problematic value:

  <option value="Speciality">Speciality</option>

My suggestion is to change the value to safe value, in this case it could be term id number.