Phone keypad allows entering "+" in unhelpful places

Ubuntu 14.10 r203

1. Navigate to the Phone "Keypad" screen.
2. Hold down the "0" key so that it enters a plus "+" sign.
3. Hold down the "0" key again.

What happens:
2. "+" remains visible on the 0 button.
3. Another plus sign is entered.

What should happen:
2. "+" disappears from the 0 button.
3. 0 is entered.

Since there is never a phone number that starts with ++, letting people enter "+" a second time is just inviting errors.

As far as I can tell, this is true for a plus sign anywhere except as the first character of a phone number.