It's just weird to use more because it's intended for interactive use, it's a human-friendly interface for when cat is cumbersome for humans to use.

The shell script, as posted, should absolutely not care whether or not it has write access to the file. There is more to this than you are revealing, I'm afraid.

Replacing more with cat on the freak theory that more sometimes prints something which causes the file it's reading to be corrupted when you run it inside backticks is the best I can offer at this point, sorry.