It doesn't look like this is strictly a moodle.org bug.
To reproduce on any site:
- Log in as admin
- Identify a block that has been added to the site frontpage. It has to be added there and not in the system context, you can't use the navigation/settings blocks so I used something like the calendar block.
- Browse to Settings > Plugins > Blocks > Manage blocks
- Find the block you chose in the list and click on the number of instances (next to the name) to get a list of all of the courses containing the block.
- You should get the notice.
I reproduced this on my integration site so I'm betting every site is affected.
Please could someone else test it and move this issue if need be.