Hello.
Today I've tried add to my list 知道 - "zhi1dao4" but skirtter couldn't find it. However skritter finds zhi1dao5
here is a deffinition for this word:
http://www.mdbg.net/chindict/chindict.php?page=worddict&wdrst=0&wdqb=zhidao
it shows a forth tone for "dao". Is this a mistake in skirtter database?