This is a typical behaviour for IR codes having a repeated part being transmitted too long. You can tweak the number of repetitions by setting the Duration of an IR code to a certain minimum. When pressing a button with a minimum duration, the code will either be transmit as long as pressed, or with a very short press, as long as indicated by the minimum duration.
Other examples of this undesired behaviour can be:
- Browsing an on screen menu by two steps at a time
- Zapping by two channels at a time