High CPU load on embedded targets caused by timers

Pressing a key (without releasing) with auto repeat enable for a longer time increases the CPU load.
Pressing a key with auto repeat enabled causes starting a timer with 600 ms.
If the timer event occurs a new timer is started with 50 ms without killing the previous timer.
A new timer is now generated every 50 ms while the key is still pressed.
Releasing the key kills only the last generated timer. All other timers stay active.