If we need to rasterize one selected object inside of the clipping group, we have to isolate the object to avoid flattening the clipping group. Isolating only the clipping group won’t help, we have to 'drill into' the object specifically!

This doesn’t happen for simple groups — with these we don’t have to isolate anything at all, just selecting a child is enough.

Thanks to Junior Rocha for raising this up.