To reproduce:
- Have a supervised user with at least two blocked sites.
- Navigate to the first blocked sites.
- While on the interstitial, enter the URL of the second blocked site into the omnibox.

Result:
Interstitial gets into a weird state, e.g. the "Ask permission" button doesn't work. Also the browser back button doesn't work, and the reload button pushes the user back to the last non-blocked page.

This applies to both legacy supervised users and child accounts. Tested only on desktop (Linux), but might apply to Android as well.