1. The fact that the sign changes. I don't like it, but indeed forcing it not to change sounds less good, which leads to:
It looks like, at least for this specific sample, the other bug with "Input can be compressed" led to bad detection and the presign change. If I work around that bug, detection and restoration are much better.
2. The fact that the 2 channels vary way too much. If left and right are pretty similar, they still should be after declipping. This is on the todo list... somewhere
That would be a quite nice feature. Strongly varying output peaks can be quite the issue on some tracks. You can work around it with a compressor after declipping, but ideally the Declipper would take care of that itself. I wish I could be of help...