After the Australians regroup after the first Japanese attack, Darko and Jack decide to find out what happened to Bluey. They both set out with rifles. However, in one of the subsequent shots Darko is clearly carrying a Bren light machine gun. In the next shot he is suddenly carrying a rifle again.
When Johnno changes Bluey's Bren gun, he takes the ammunition from the gun, and after he is almost hit by a bullet, he takes it off again.
When Jack trips and falls face first in the mud, as he crawls and struggles to get back onto his feet you can see his rifle bend and wobble. It's a rubber prop.
When Darko and Jack are creeping through the bush, you can see a figure run past in the distant background. The director admitted in the commentary that the figure was his safety officer running for the toilet.