OECD model tax convention: changing residence mid-month

OECD model tax convention and its commentary serves as a basis for many Double Taxation Agreements between European countries. How, typically, is a person P taxed according to the tax convention in the following case:

• P is a resident of country A according to the convention from Jan 1 until Aug 15
• then, from Aug 15 until Dec 31 they are a resident of country B
• they derive income from employment which is exercised in the corresponding states (A until mid-August, B afterwards)
• they receive salary at the end of the month (ie. Aug 31)

Should the August salary be taxed only by the country B (which is the country where P is a resident when he receives the salary) or half-half between A & B, as P already earned half of their August income when they became a resident of B?