Is this a proper use of unless. Does it make sense and what does it mean exactly?

Here is the sentence (from sentence 2):

1: What if the printer prints the pages in random order?
2: It shouldn't print like that, unless it's malfunctioning.

Is the second sentence correct, can you reword it and explain it? I want to make sure that it's a proper use of "unless". Does it also make sense when applying the second sentence to the first?