Another user made some commits to a project we collaborate in. In their git client's global settings, they were using my email and name by mistake. However, they made all the commits using their own SSH key (which was correctly tied to their account on BitBucket).
Right now, if you go to the project Overview page, you see those activities are attributed to them (their name is listed next to the hashes), but if you go to the Commits page you see my name listed.
I'm marking this as major, because it is affecting one of the major parts of a version control system: understanding who did what.