One of our employees just stumbled across this. We’re using Spark 2.5.8.
To reproduce the issue:
Open up a target user’s chat window.
Click the “View information about this user” (Profile) button.
Now, open your own “Edit My Profile” screen.
Then, the “View full Profile” button back on the target user’s chat screen.
Finally, press “Save” on your own Profile Screen.
You will adopt all their profile settings, including the avatar and display name.