Transform DWG Files with External References - leave reference insert points untouched

Hey - I have to transform a lot of DWG Files into a custom coordiante system. The transformation works, but I have a problem doing so when a file has external references (in this case the reference points to another DWG in the same directory, which therefore has to get transformed as well). Following my first thought, I tried to transform all files but leave the insert points for the references untouched, but this didn't work. Even when discarding the RealDWG reader Option "Read External References" or trying to filter out everything that has the value "autocad_xref" for autocad_entity with a test filter and letting these objects bypass the transformation process in my workbench, I'm getting the same result: The insert points for the references are transformed too and therefore seem to be shifted double the distance in comparison to other objects. Do you have any advices for me how to solve this problem? Thanks a lot! :-)