Request needs to be said twice to obtain reply

[didfem 0]

I couldn’t understand why the P2ATC Copilot often did not acknowledge the controller’s clearance or request, such as a takeoff clearance or a frequency change. This happened frequently, but not always. Today, I found out that if I repeated the very same request, exactly the same way, I would get once more the controller’s reply BUT, after this second time, the copilot would acknowledge the controller’s statement and the exchange would continue normally from then on. This is puzzling. My work around does the job, but I sure would like to know why I have to go through this rigmarole...

Didier