I cannot reproduce the model saying it is Claude if I have Gemini selected! You can always sanity-check which model you are talking to by seeing it “thinks” and specific to Gemini, see if it thinks after every action (think → reply → edit file → think again, etc).
We are currently seeing some weird issues with Gemini 2.5 but we don’t currently see an issue on our end. See this thread for ongoing discussions: