Submission file type changed after upload

Alex.B.4366

I've had a strange experience wherein I uploaded a .dwg file (as a submitted assignment), then a .dxf file in the same assignment.

I then deleted (moved to the trash bin) the .dwg file on the computer. I left both files on Brightspace.

When I next looked at Brightspace, both were listed as .dxf files. Can anyone tell me how this could have happened?