JSONRPC GUI.TextFieldSet fails on Search/URL Bar

When sending the following command and "failed to execute method" is received when the text cursor is in the Search/URL bar (not dialog box).

SendTCP: Sending - {"jsonrpc":"2.0","method":"GUI.TextFieldSet","params":{"text":"charmedquark"},"id":0}
SendTCP: Response - {"error":{"code":-32100,"message":"Failed to execute method."},"id":0,"jsonrpc":"2.0"}

Keyboard displayed state is true, which is the only indicator in JSONRPC to tell us when we can submit text:

{"id":0,"jsonrpc":"2.0","result":{"state":{"displayed":true,"password":false,"text":""},"success":true}}