Viewing this page in Chrome and Safari will present no problems—each button will appear just like it's neighbor.
However, in Firefox, prior to v30 (coming in June-ish), the last two buttons will be shorter than the first two. This is due to Firefox's overly specific line-height on input buttons.
You can address this by avoiding line-height in your buttons and using only padding for vertical spacing. If this works for you, great, but I'd still recommend using <button> elements everywhere.