Not a bug.

It wants your HP to be a prime number (the boss will specifically say "compute vitals to primes" or something to that effect).

1 isn't a prime number.

Going by what's usually touted as a prime number (divisible only by itself and 1), I feel like it should be; that or the commonly touted "rule" should be revised.

But much like how some people think November should be considered part of winter, what we want or think should be the case doesn't necessarily change what is.