Well, what I needed was to find out whether the corresponding process is running on the machine when avast is active (according to a download from HP, the process would probably be HPKEYBOARDx.EXE or Keystatus.exe).
If the startup of the program were blocked, it might have been a problem of 5.1.864 (and of course, its icon(s) wouldn't be shown in that case, but that's basically just a side effect).