iRules and Data Group

I am trying to use DataGroup in iRules. I need to block a list of User Agents would like to use Data Group. Local Traffic|iRules|Data Group List, I created a Datagroup called UnwantedAgents, the type is string, and create useragent01, ... useragent15. I leave empty on the value when I create records.

Then when I update the value to agent string, the record is gone. For example name:useragent01 value:cssutils+0.9.8a3+(http://www.cthedot.de/cssutils/)

After I clicked Update button, the useragent01 is disappeared from the list.

Why? where is this record? I am trying to add new usragent01 record, I got the message said the record is in the list already.

Did I do something wrong?

Where is the file stored?

Thanks, Xin