Not seeing that behavior here. Five A/V linked clips were dropped onto the timeline; they were not grouped. A portion of each was deleted. This excised both audio and video.
Clips 1, 3, 5 were unlinked, then selected and dragged to audio track 2. Each clip retained its original length.. No need to relink, but it made no difference in clip lengths.
The volume on track two was maximized. The project was exported, and volume on all track 2 clips remained maximized.