We need to compare 2 versions of the same model in Autodesk Forge web viewer. Both 2D and 3D models, and in different formats (IFC, DWG, Revit, ...). The DiffTool extension works mostly fine, but there is a problem.
We are using the Autodesk.Forge C# library based on this example, but it is generating a "Source File" attribute for every element in the model.

This then is marked as change in every element during the comparison, which is not wanted. 
I managed to track down where the attribute is coming from, and it is this line, namely the second attribute of the UploadObjectAsync function:
uploadedObj = await objects.UploadObjectAsync(input.bucketKey,
/* here -> */ Path.GetFileName(input.fileToUpload.FileName), (int)streamReader.BaseStream.Length, streamReader.BaseStream,
"application/octet-stream");
I tried to override the parameter and set it to a fixed value. That way, the "Source File" attribute would be the same and would not show as a change. But that didn't work, since the attribute is "object id", setting it to a same value as a previous model caused the new model to override the old. So even if I used the old URN, I would see the new model.
So, is there any way to solve it? Do I have abandon this C# library and do the REST API calls manually with curl or something? How to solve this?