I noticed two errors in the current version .23 (I think they existed before):
Beat does not save the selected instrument. This means you switch from one song to another and the default instrument is selected. E.g. SN instead of block.
When I create a new song and the option “Preferences/Layer/No Default Layer” is selected, then only the first part does not contain a layer. All other parts contain the default layer.
The same thing happens when I add a new part to a song. A default layer is then created.
You are correct, add Part will create a default Layer despite the preference. WIll be fixed with the next version.
It should be noted that this rule only applies as long as no default Song or Part has been saved which contain one or more Layers. “Save Default Song” and “Save Default Part” will be called with every add Song, or add Part resp.; they will load the saved default as saved, regardless of the preference.