That's why managers should never sign anything an applicant or employee hands them without prior HR approval. Better yet, have an attorney review any such documents. Employment contracts should be drafted by someone who represents your organization's best interest, not by employees.
Recent case: During Robert Baum's job interview with Helget Gas Products for a sales position, he told the company president and another manager that he needed a three-year contract. Baum took careful notes of the discussion, including the company's descriptions of his expected salary, bonus payments, job duties and benefits. After he accepted the job, Baum took his handwritten notes, wrote "Contract with Helget Gas Products" across the top and gave them to the manager, who signed the notes.
A year later, the company fired Baum for not meeting sales goals. He fired back with an employment-contract lawsuit, alleging that the company had guaranteed him three years of work. Unfortunately for the company, a court found that the notes signed by the manager did create a contract. The interview notes were silent on the issue of sales targets. (Baum v. Helget Gas Products, No 05-2142, 8th Cir., 2006)