The bug is that it shows they character as entered into the passcode when it really isn't. The bubbles should only update when you get lift your finger, not when you initially press it down.

> The dot for the typed character appearing immediately is different from alphanumeric keyboard behavior, because you can't register any key press before releasing the touch (or key) there, due to composition.

That is exactly why the dot should not appear immediately upon the down event.