When Luke & friends are in the trash compacter, a squad of stormtroopers bursts through the door to the control room where R2 and 3PO are hiding.Which "head bumping" stormtrooper are you referring to? I don't quite recall that one.
As they walk in, in the right of the frame, a taller stormtrooper extra quite obviously bumps his head on the top edge of the door frame. It just so happens that as this occurs the center trooper says "see to him" leading to an accidentally comical moment.
Fans have pointed out this gaffe for years, so much so, that in 2004, Lucas added an extra "bong" sound effect to the moment and "canonized" it by claiming, in the same audio commentary, that this was a genetic defect inherited from Jango Fett. In Episode II's DVD audio commentary (released in Nov 2002), during the scene where the Slave I is taking off from Kamino after the fight between Obi-Wan and Jango, we see Jango bump his head on the top of the door in the ship as he gets inside... and Lucas mentions this as well.
As far as the "incoherence" I wouldn't say that the voice was ever that big a deal. Lucas created this inconsistency when he decided to do the backstory and presentation of Boba, invent Jango, and the Clones-Stormtroopers connection. Now we've got people asking when Lucas is going to dub over the stormtrooper voices and other vigorously defending that they're not all Jango clones, or clones of anyone for that matter (to save the extensive EU materials that clearly never considered this possibility). It just sounds stupid now, and slaps you in the face with a reminder that Episode II and III exist now, every time you watch those scenes.
As for me, I dislike both the contradictions introduced by the Prequels AND shoddy presentation. The movie shouldn't have to suffer because Lucas made the story up as he went along.