Compiler showing 'pi' symbol on error

Question:

I was testing some code on Coliru, and I got a strange output. I went down the code and could reproduce it with this simple piece of code:

int main()
{
    π
}

The output on g++:

clang:

For instance, using just pi (without the address-of) shows the expected result:

main.cpp:3:5: error: 'pi' was not declared in this scope
    pi;
    ^

I tried to reproduce this on my machine, using g++ 4.9.2 and on others sites but I could not.

Is this some bug on this site, some config of these compilers ?

And why only using the address-of operator (&) shows this symbol ?

Answer:

It's a bug on the site, as the compiler's output is not properly escaped. The compiler should output π, but that's valid HTML, producing the pi symbol you see.