I'm no web-dev, but shouldn't these things be sanitized server-side? In which case, except for the mobile keypad issue, all these problems would solve themselves? And shouldn't they be doing this anyway?
Server side sanitisation doesn’t address any of the accessibility concerns. Server side sanitisation doesn’t address the silent dropping of characters concern. Server side sanitisation doesn’t address the incrementing/decrementing the value accidentally concern.
That’s because the issues being discussed here are about creating a good UI that minimizes errors, and has little to do with sanitisation.