Same gravatar is displayed for different users in stackexchange.com [filters page](https://stackexchange.com/filters/118502) under the "Top Network Askers" in the right side bar. 

The free hand circled image's source are from `https://www.gravatar.com/avatar/?s=18&d=identicon&r=PG&s=30`. Seems the gravatar id is missing in the image source.

For an example from the list, the user Mad Scientist's gravatar id should be `https://www.gravatar.com/avatar/66c66c4d97a7bc3859a85253f003e1fb?s=18&d=identicon&r=PG&s=30`, but is mapped with `https://www.gravatar.com/avatar/?s=18&d=identicon&r=PG&s=30`, which caused the display issue.

> [![Same gravatar][1]][1]


  [1]: https://i.sstatic.net/TvLk6.png