The close button (X) on the titlebar doens't close the application, yet it is shown.
When you click the Close button, Tux Paint should (at least in the normal canvas screen) pop-up an "Are you sure you want to quit?" dialog, which seems reasonable. Are you not seeing this? What's the exact situation?
Also, are you using the latest version of Tux Paint? (When you created this bug report, you listed version 0.9.14, which is very, very old at this point.)
I am using Tux paint for a long time, some days before i downloaded the code. I found it as much interesting, since most of the programming language used in this marvelous application is very known to me. I have introduced this software to the school where i had studied, they were impressed and now they have installed tux paint in lab and most of the students likes it! So it would be great pleasure for me, if concerns gives me a chance to fix this bug.
Even though i am doing the Tux paint's code part for the 1st time. I will try my best to fix this bug.
No response from reported, so closing.