The current implementation of IR code recognition is only able to detect complete IR frames (65 level changes). However many remotes send the complete code only once per keypress. If the key is held for a longer duration a special repeat code is sent. NEC IR Protocol
This doesn't get recognized by the current routine and even if it were the interpretation of the repeat code isn't completely trivial. I.e. some in some commands a repeat doesn't make sense (mute) in some it makes more sense (preset +) and in some it makes a lot of sense (volume +/-). It even might be confusing to some users if this functionality is missing, as the standard behavior of consumer electronic devices is to increase/decrease volume as long as the rc button is held.