The rules of the stargate are quite strange and often "expanded" to create some plot. But I give them that their explanations are often quite clever.
A third point is that a stargate actually has a way to recognize objects. It only sends the object if the whole thing passed the event horizon. Otherwise it just would rip people and stuff apart when they try to pass.
I've never figured out what is really supposed to happen when you shut off a worm-hole in mid-transit. In one episode of SG-1, some heavy material re-materializes inside of the nearby planet's sun (causing/solving the red sky and eminent doom). In another episode, Teal'c is trapped inside of the buffer, and his atoms are not just randomly lost at some point in space between the two gates. Also, there is at least one episode I can recall where a Jaffa retreating through a gate has his staff weapon cut in half when the gate shuts off. Also in the 2nd episode of the entire series of SG-1, Kawalsky had his head cut in half by them shutting down the gate while his head was partially in the wormhole. So the whole thing about transporting entire objects as one packet seems to be not true all of the time.
Bus error -- driver executed.