Just going to add this to your current report,
http://feedback.dayzgame.com/view.php?id=25468
The toggle of Firearms mode indeed worked in version .55 and back, but as of the current stable .57 the toggle no longer works and from what i gathered all firearms are no longer are able to change their "Firing mode" such as both the IZH-43 and Blaze will now only fire 1 bullet regardless on how many times you toggle the "T" button.
Also will upvote this as well for this suggestion is indeed needed to be able to at least know what the current firing mode is at when the firearm is toggled.