On rerun, faded elements are becoming opaque one by one. Instead they become opaque all at once.

Steps to repro:
1. Run `examples/reference.py`
2. When done, rerun it.

**Expected:** on rerun, all elements fade out and then become opaque one by one even before the run is done.
**Actual:** on rerun, all elements fade out and only become opaque when the entire run is done.

I believe this bug was introduced with the Sidebar code.