Didn't notice any bugs, but haven't tested for bugs. Used it and it works great - favicon.ico is much small than that other thing I used in http://nashape.com/blog/2012/09/12/big-favicons/. Great work! (especially because you did it in PHP which, after 10 years, I don't think I can face again...)
I actually left that browsable on purpose, i thought browsing other peoples favicons would be something quite interesting. Its not something i feel needed protecting.
Edit: Really good article on the subject: http://dcurt.is/pixel-fitting