If you went to sleep and left your phone in a browser window or you have been browsing for a while and all of a sudden you are taken to the Mpesa menu, then you are not alone. To address the problem update your Mpesa menu by going to Mpesa >My Account>Update Customer Menu.
This issue normally occurs if you have a phone that has been in existence for years.
Let us know in the comment section below whether this addressed the problem.