To me it suggests that if you have used a third-party style recently or, someone else has used your keyboard, it could be the way theirs was set and was in the memory of the keyboard when it was switched off.
We take turns to bring our keyboard to our Club and this has happened to me on several occasions when the last person to play my keyboard had used their own SD Card. As you've discovered, the easiest way to deal with it is to 'initialize' the keyboard itself.
Audrey