A Google Web Search Help forum has confirmed reports of a bug with Google's home page prompt to request users to make Google their home page, specifically with Internet Explorer.
The issue is, even if Google is your home page, Google is asking those users to make Google their home page.
One searcher said:
Google is already my home page. However, it won't be for long if I keep getting a banner asking me if I want it to be.
This is not the first time Google's homepage prompt request annoyed users.
That being said, Googler Sarah said they are aware of the bug and working on a fix. She said:
Just wanted to let you both know that in investigating this, it is a known issue that we are working to resolve. If it helps, this is currently only for Internet Explorer so using another browser will help negate the frustration.
Thank you for your patience!
Forum discussion at Google Web Search Help.