Weird analysis behavior

[nkrusch]

int main(int a, int b, int p, int q, int q_) {
  while (true) {
            a = a + 1;
            b = b + 1;
            q_ = a + b;
            q_ = q_ + 1;
            q_ = q_ * p;
            // q = q + q_;
  }
}

With the last line commented out vs. last line included, the second case takes 10x longer to run the analysis. I would like to understand why. Not sure if this is machine-specific.

The second case is infinite, but there are similar examples without infinity, so that should be irrelevant. It may be something stupid, like "copying lists in Python", but in any case looking for this kind of explanation.