Thanks for the quick answer!
About the system sound increasing issue, I made some more tests:
(from the calling phone) letting the call stop ringing by itself does not reproduce the issue; hanging up the call while ringing makes the sound increase.
I've tried changing my sound settings (system sound at 20% and volume sound at 60%) without any effect.
I've also noticed that receiving a call to ignore, if in stand by mode (screen off), the phone wakes up (screen on) making the already mentioned "answer key blinking".
About the folder (I'm sure it's me): could you provide me an example of the string inserted in "to folder" field? (if works I will use
your folder name

)
I'm running the original italian HTC ROM on the Touch PRO.