Excel is interpreting like a number everything that looks like a number - just like your id. And since it has limited numeric presicion (about 15 significant digits), it looks like the last digits are replaced by 0 (in fact, the whole number is rounded).
To avoid this, change the cell format to text before pasting and use Paste special... -> values only.
For CSV it might be sufficient to enclose the values in double quotes, though I'm not 100% sure about this.