Trim not working reliantly

Hi,

I'm trying to work with the trim with region(s) component, but it is just not working reliantly.
If you set the sliders in my file to tArc:0.21 and Radius:0.007 for example, it won't cut the circles properly. This also happens with a few other combination. Sometimes the circles will vanish or won't get trimmed.
Does anyone know, why this happens or is there any other way to trim the circles? Or is this a bug?

Thanks in advance!