What Every Computer Scientist Should Know About Floating-Point Arithmetic

Not a bug, it's an artifact of a finite number of bits being used to represent an infinite concept. It's also covered in perlfaq4 under the heading "Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?"

And if you want excrutiating detail on the issue, look at perlnumber.