Nested "For Loop Container" causes the outer loop to end

I have an abstracted project consisting of a "For Loop Container" within another "For Loop Container". The definition of the outer loop is:

and the inner loop is:

The default value for @QuitLoop is False.

Within the inner loop I have a script task which reports the values of the @OuterLoop and @InnerLoop variables and I get 100 messages:

However, if I add a step in the script task which sets the @QuitLoop variable to True at a certain point:

if (iOuterLoop == 2 && iInnerLoop == 4)
{
    Variables vars = null;
    Dts.VariableDispenser.LockForWrite("User::QuitLoop");
    Dts.VariableDispenser.GetVariables(ref vars);
    vars["User::QuitLoop"].Value = true;
    vars.Unlock();
}

both loops stop running at this point:

However the @QuitLoop variable should only impact the inner loop. Why would the inner loop be causing the outer loop to stop early?