NRF24 Thinking-Break

Hello,

My NRF24L01 gives himself a thinking break, when it had a break already.

In detail, if I continously feed the sender with data like here
https://arduino-info.wikispaces.com/Nrf24L01-2.4GHz-HowTo
all data gets transmitted stable, without any doubts or issues, continously, in "High-Speed", for hours. .

But when I put a delay command in the loop

void loop() /****** LOOP: RUNS CONSTANTLY ******/
{
joystick[0] = joystick[0] + 1;
joystick[1] = joystick[1] - 1;
radio.write( joystick, sizeof(joystick) );
delay(25);
}//--(end main loop )---

Transmission hangs from time to time..
I figured out that when I thinks it hangs, the "radio.write()" needs 500 ms to get executed - but just accidentally, not each time.
I can provide more code or evidence, but may be this all already known, so I don't want bother you for current.

Any ideas what's happening here?

Martin