Lush supplies a spell checker in the editing mode, even poems benefit from a good spell check before submission. You should have one last check, specifically after you have made any changes. It's just a good habit to form.
Poetry line breaks are so important, as well as just general spacing. Hard line breaks that you have made on your computer can cause glitches in the submission process. You may not even notice them in the presentation on your computer. It confuses the Lush final formatting process. Lots of people experience this. I know I do. Check the final presentation right before you submit. Sometimes you have to go back and edit to remove hard line breaks 2 or 3 times, don't settle. Usually for me, the third time is a charm. During the 3rd time, the glitch seems to disappear and spacing and line breaks are as you intended.
No system is perfect. Have your poetry laid out how you want it to be read by the reader. It determines the emphasis, pauses and speed of the reader. Remember too, every poem without stanzas does not have to be double spaced. Removing the double spacing often looks better on the page and increases the readers speed (which may improve the poem itself). Sometimes I like a reading that pushes forward because it builds momentum for the main thought presented at the end. If there is rhyming, removing the double spacing (when you do not have stanzas) works well for increased flow of rhythm.
Once again, there is no hard and solid rule regarding line stops and spacing on LUSH. Of course, double spacing should be between stanzas. That's just general knowledge.
But seriously, think of how all of this controls the reading of your poem. Use it to your benefit. Sometimes listening to your poem being read by a 2nd party is good. It could be the difference between a poem that reads like "blah blah blah" and a poem that excites or pulls your reader in. It is also a visual representation of a mature poet.
Of course I'm not mature, but I like to look like I am.
