Unable to reproduce. Check on your end regarding input device. There are at least two scenarios where this can occur that I'm aware of:
- using key/button macro type program to send backspace character on action
- 4+ button mouse, where default side buttons send backspace character code. If you are accidentally pressing the side button or the mouse is worn down and the side button is pressed internally when other buttons are pressed or when housing is squeezed in a certain way.
Form submission is not governed in any sort of way that would be differentiated by browser or other client configuration. Form only goes one way. If it were to happen to one person, it would happen to everyone.