I'm recording radio with radiomode better. There is very often a file called original.dash.m4a as well as the original.m4a file. Any idea why this is happening?

Something on your system prevents the dash.m4a file from being removed after it has been remuxed to another file. Since it would seem the final output file is OK, you can ignore this and delete the dash.m4a file. Feel free to follow our instructions to provide a proper report so we can see what is happening on your machine, but there is no guarantee it will shed any light on something that is peculiar to your system.