I had the same issue where I couldn't enter more than 3 characters for the account number. The accepted answer is correct in that there was a weird hidden character that was place when I tried to copy/paste the account number.
How I fixed it was by CTRL-A to select everything in the textbox then Backspace/Deleting everything in the field. After that I was able to manually input the Account Number as usual.
Hope this helps!
