One Bug of WatiN?

With WatiN,How to find a radio input button on the page?
such as the line of HTML:
<input type="radio" id="rdb_1" name="rdb" value="Value_1">
How to get it?
1) ie.RadioButton(Find.ById("rdb_1"))
2) ie.RadioButton(Find.ByName("rdb"))
3) ie.RadioButton(Find.ByValue("Value_1"))
neither of  these methods works well.
Now I can only get it with this:
ie.RadioButtons[index]

Why do them?
May I get some suggestions?