The gemara says that if a husband would make a shliach to bring a gett to his wife (shliach l'holacha), and then the wife would turn him into her shliach to receive the gett (shliach l'kabala), the gett is not valid because the shliach is not able to return to tell the husband he did the shlichus. What does this mean? Rashi explains that the basis for this concept is:
שליח שחזר ונעשה שליח למי שנשתלח לו ניתק משליחות הראשון עד שלא היה לו שהות לחזור אצל שולחו ולומר עשיתי שליחותך
Both the Taz and Avnei Miluim (E.H. 141) explain that by becoming a shliach l'kabala he looses his status of shliach l'holacha, and therefore there is no time between being his shliach and her shliach to report back to the husband that he did the shlichus. Based on Rashi, the shliach who accepts status of shliach l'kabala, will loose his prior status of shliach l'holacha, and therefore even if he decides to hand the gett into her hand, she will not be divorces - since he is no longer a shliach l'holacha. However, the Rambam clearly writes that under these circumstances she is not divorced by the shliach becoming her shliach l'kabala, but as soon as the gett would be given in her hands she would be divorced since the shliach would retain his original status of shliach l'holacha. In short, Rashi and Rambam argue whether the issue of the shliach not being able to report back prevents him from becoming her shliach l'kabala but he retains status of his shliach l'holacha (Rambam) or does the acceptance of becoming her shliach l'kabala make him loose status of shliach l'holacha so that even if he would decide afterwards to give the gett into her hands she would not be divorced (Rashi).