In my project, there is something called creating tasks. Upon creation of tasks and I close the page, system prompts me an alert "You are about to close this application and save all changes...."
followed by an OK and Cancel.
Using F12, am unable to detect neither the alert nor the OK/Cancel buttons. Please take a look in the image uploaded.
Personally I have never worked with alerts in tests so I might be wrong, but I think that keyword Handle Alert should be helpful for you.
http://robotframework.org/SeleniumLibrary/SeleniumLibrary.html#Handle%20Alert
Could you please try with Dismiss Alert or Confirm Action
For more details check the below link
http://robotframework.org/Selenium2Library/Selenium2Library.html#Dismiss%20Alert
Confirm Action
http://robotframework.org/Selenium2Library/Selenium2Library-1.8.0.html#Confirm%20Action
Try with the below keyword
Choose Cancel On Next Confirmation
