I see nothing behaving as it shouldn't. You probably think that the aux send should also be affected by the track gain, which would happen if the send was post-fader, but it's pre-fader; see this diagram as reference: https://www.rncbc.org/drupal/files/qtractor-aux-send-plugin-1.png
So, since you don't need the dry signal at all, you could keep the send at the desired level and lower the track gain to the bottom or, as I suggested, simplify workflow and routing via direct bus output selection.
I see nothing behaving as it shouldn't. You probably think that the aux send should also be affected by the track gain, which would happen if the send was post-fader, but it's pre-fader; see this diagram as reference:
https://www.rncbc.org/drupal/files/qtractor-aux-send-plugin-1.png
So, since you don't need the dry signal at all, you could keep the send at the desired level and lower the track gain to the bottom or, as I suggested, simplify workflow and routing via direct bus output selection.