int main(void)
{
    int a = 42;
    return 0;
}

Building this with gcc gives the following output:

main.cpp: In function 'int main()':
main.cpp:5:9: warning: unused variable 'a' [-Wunused-variable]

This is a single warning. On the sidebar (the Build progress) the number 1 is displayed, and same for the badge on Issues label.

Filtering out warnings removes the badge, and unfiltering them displays 2.

I also somehow got negative numbers on the badge (without any filtering/unfiltering) on subsequent build, but I can't currently reproduce this.