Hi Felix
I assume you are asking if Mkgmap can detect the error, 
but for others who may find it helpful… 
the JOSM validator will give a warning for Overlapping highways and if you select ‘Overlapping highways’ it will highlight them.
You can then zoom and select. The middle mouse button will list the ways and relations and middle mouse button +Ctrl will all enable selecting of individual ways.

 
On 20 Mar 2018, at 10:37 AM, Felix Hartmann <extremecarver@gmail.com> wrote:

Is there a way to detect such an error?