In recent years, several MAC (Medium Access Control) protocols using directional antennas have been proposed for mobile ad hoc networks (MANETs) including our proposed MAC protocol called SWAMP (Smart antennas based Wider-range Access MAC Protocol). These are typically referred to as directional MAC protocols. This paper first summarizes the proposed directional MAC protocols and outlines these common issues, which reduce the probability of successful transmissions, such as location information staleness, deafness and directional hidden- and exposed-terminal problems arisen due to directional transmissions. This paper formulates and analyzes the issues of directional MAC protocols, and proposes solutions of these issues, especially for location information staleness. The experimental results show that the mobility prediction and the optimization of parameters associated with location information staleness, such as the beamwidth and lifetime of the table information, may mitigate location information staleness and improve the overall network performance.