Normal behavior:

1. Load chrome://md-settings
2. Click "Manage search engines", notice how it expands smoothly.
3. Click the left arrow button within the section, the section closes normally.
4. Click "Manage search engines" again, it still expands smoothly.

Degenerate behavior:

1. Load chrome://md-settings
2. Click "Manage search engines", notice how it expands smoothly.
3. Click the left arrow button within the section, the section closes normally.
4. *Use the browser back button* to re-open the section. The section immediately becomes taller before playing the expand animation, instead of animating smoothly.

Similar things happen using the back button in step 3 and the forward button in step 4. It's very weird that different ways of triggering route changes cause different animation behavior.