Wow, no response. Okay, maybe someone will still get some use out of this.
I just submitted using Libre Office(same people, very similar program: actually recommend it over Open Office now).
It seems to have some issues reformatting lines. Basically prepare your manuscript: with the Header/Courier 12pt font, lines up to 70 characters(which on courier is like a standard margin width in most word processors). Make sure you've formatted your paragraphs appropriately either with 5 spaces, or with lines between each paragraph.
Then save as .txt, you can try choosing encoding if the option is available, but in my experience none of the Libre Office doesn't seem to save paragraph indents properly. There's no helping it.
Proof-read the .txt file in notepad to make sure there's no funny characters.
Feel free to check the result here:
http://www.critters.org/c/mscheck.htDespite getting format messages about short lines, when I got to see the 'estimated' final product after submitting, it actually looked properly done.