Ok, if you need this you could go another way:
Currently you could setup your form to hide alle of the actions with 'no data actions' enabled.
Then add a button and assign a frontend function to it. The frontend function just needs to save the form:
app.record_save();
I know that it not the most pretty way - but we want to improve the form buttons with the next large release (REI3.8). Hope this is a useable workaround for now.