I think you've just insulted a lot of people. I've run into the backspace behaviour multiple times and never on purpose. Here's a few reasons why it can happen, apart from stupidly mashing my keyboard, which I assure you, doesn't happen very often:
- touchpad not registering a click on the text field
- element reloading due to weird js and losing focus
- tab switching properly between the first 4 fields, but then focusing some random button instead of the 5th input
- broken custom JS elements which don't quite understand focus and editing
- general keypress hijacking which doesn't do what you want
I don't look at the keyboard as I type and I don't always look at the screen either. I expect the text actions (input and editing) to work on text. If I have to think about which possible, implicit mode I'm operating in, it's a bad design. Or are you saying that before every keypress you visually verify where your cursor is, is it blinking, is the right window focused, are there multiple cursors with fake focus, etc?