Each DT400 can be set up to operate new decoders selected by that DT400 as any decoder status code you choose.
New decoders are defined as decoders that have not been selected in your system.
Your DT400 is set to expect to operate mostly decoders that are 128 speed step capable, so when a new decoder is selected the DT400 defaults to that status code.
If you operate mostly decoders that are only able to recognize 28 speed steps, you can change this setting.