gnome-calculator displays incorrect results after Ctrl+Z

I am using Ubuntu 13.04, the gnome-calculator is at 3.8.1 and displays incorrect results after doing a Ctrl+Z.

Steps to reproduce:

1.- Enter an operation, i.e. "3*3"

2.- Press enter, result is displayed correctly in bold face: 9

3- Enter an additional operation, following the previous result, like: +2, the calculator display will show 9+2

4.- Press enter, result is displayed correctly in bold face: 11

5.- Press Ctrl+Z, this will return to the previous calculation: 9+2

6.- Press enter, result is now incorrect, now it indicates in bold face: 13, instead of the correct result of 11.

In this scenario, pressing Ctrl+Z, followed by Enter will continue increasing the result by 2

I do not think this is a desired behavior.