if you have truly stripped out all HTML code, all embeds, and have a single entries tag with a single entry showing, and the default comment code outside of that entries tag and your details are still showing in that form then i can only think it is:
1. You not logging out from the front and back end correctly - either the session or cookie is not being destroyed (but you hitting logout button, or the browser is ignoring you)
2. You have a plug-in doing something funny with the processing of comments.
As i created a stripped out test version and could not replicate your problem. Therefore i have to assume it is something local to you causing the issue, i.e. browser, your template code, your methods, or plug-ins.
You are on the most up to date version of EE i assume? Revision and build i mean? Including updated template files too for the control panel, etc.???