It happens to me regularly. I bite the bullet,
1. set staff to 100%, then set staff to auto recruit again.
2. raise salaries by 3%.
3. increase marketing budget by 25-50% for three months.
There is the balancing function but it's tough to make work properly, needs Auto-Recruit OFF before moving aircraft, then I forget to turn it on again, and there's always one or two staff get added later to serve the additional office work.