Overwriting others?

hello

I tested it shortly with birds/cats and unfortunately see that there ware available (not earlier generated) avatars overwritten. That would my users not like ??
My Avatars come from Gravatar and from Plugin “WP Social” by registering.

For now I go back to Identicon (Generated) because it is not so invasive, seems that only those manually uploaded stay untouched.

The page I need help with: [log in to see the link]