On the donation screen you cannot enter numbers unless you first use the slider bar to generate an amount in the donation box. You can then edit this amount to the required figure
I have the same problem. When you click and enter a digit in front of the default 0 it disappears and the cursor moves to the right of the 0 in the box. Running chrome Version 49.0.2623.112 m as i am using Windows Vista - Home Basic
I also had this very annoying problem, the good news is that since this latest upgrade the problem appears to be fixed, the "0" now accepts other numbers, so i guess its fine now.
Thanks to those who fixed it.