More tests.
I tried setting the output of the bus drum to a new audio track and recording the output as the song played. The resulting recording is quite different from the audio I hear, a relevant amount of the high frequencies are missing, along with transients and part of the stereo image. When played back along with the drum bus I can clearly hear it yields an important residue.
I have reopened the project in Cubase 7 Elements and made a new export from there. The error is smaller but still evident, the 2 tracks don’t cancel each other out either.