Why does select-word-style stop me from using backward-kill-word for leading whitespace?

If I have just some whitespace at be beginning of my zsh prompt, I can usually ^W (backward-kill-word) it away. However, as soon as I load select-word-style - even if I don't select any special style - this doesn't work anymore. When I select-word-style shell it works again, but that's not the style I want by default...

Is there a way to avoid this annoying behavior? Of course I could create a custom widget which removes the whitespace if necessary and otherwise calls backward-kill-word, but that feels like a pretty dirty solution.