As far as I can see, the head shrinks back to normal again after the barrage has stopped, yes?
The problem is that the head keeps shrinking past that point to noting, and then re-enlarges upside down, as if the "minimum head size" is a negative value of "maximum head size"(?) Then you have to shrink this head and re-inflate it the right way up to score a kill.
However, I know nothing about coding so could easily have this completely wrong.
The model I have to say is really great - It has the old U4E style with all the added detail and curves and shiny bits to make it fit with UT2k3. Quite why a gun that fires bubbles needs such a huge (yet stylish) cooling jacket is anyones guess, but it looks great all the same - particularly the 'detergent bottle' ammo cannister on the back.