I had to screw up DB data consistency for another case, and when tried to reproduce that case I've spot this wrong behavior below.
Skew up DB - a hosts uses template's ID in proxy_hostid field.

Attempt to delete the template.
If an update operation performs 1st step which is successful (template unlinking in my case), then report is Green, while if you expand it, you see SQL error:

Any changes actually not made, so it falsely said it was successful. This is key point of current issue.

If the template in not used for any host and the update operation does DELETE SQL as 1st step, then report is properly Red: