该CVX警告是什么意思？

Question

当我运行以下CVX代码时，收到一条我不明白的警告。我只有警告，然后代码返回了解决方案。而且，如果我重新运行代码，就不会再有警告了。

警告是

Warning: A non-empty cvx problem already exists in this scope.
   It is being overwritten.

代码是

v = [1;0;1];
efms = [1, 1, 0; 0, 1, -1 ; 1, 0, 1];
irrev = [1 2 3];

cvx_begin
    nefms = size(efms,2);
    nreac = length(v);
    variable lambda(nefms,1);
    minimize(norm(lambda,2));
    subject to
        v == efms*lambda; %v = sum(li*efmi)
        for i = irrev
            lambda(i)>=0;
        end
cvx_end