In duplicate bug 1051828, Michael Muller makes this point:
"After applying updates via update-manager, a window pops up which tells the user to restart his system. Unlike most windows, there is only a "ok" button but no "cancel" button. This may confuse people as they just click the button to kill that popup window (but actually, he just told his system to restart).
Therefore, there should also be a cancel button in case one does not want to restart his system."
In duplicate bug 1051828, Michael Muller makes this point:
"After applying updates via update-manager, a window pops up which tells the user to restart his system. Unlike most windows, there is only a "ok" button but no "cancel" button. This may confuse people as they just click the button to kill that popup window (but actually, he just told his system to restart).
Therefore, there should also be a cancel button in case one does not want to restart his system."