As specified in the CEF, new lines in the extension must be encoded as the literal \n or \r. Upon receiving these, instead of converting them in LF or CR, the plugin further encodes the backslash rendering it \\n. If instead of encoding the new line you send it as is, the plugin treats is correctly, which is also wrong since the message should be invalid.

As for the version, current release on a fresh install with stock settings.