So most Kindle owners downloading the book have gotten a badly formatted text.
Elizabeth Castro http://www.elizabethcastro.com/epub/, I think it is, has some suggestions re how to "correctly" format poetry. A general problem with poetry is that it should in theory indent on wrap, not outdent. What to do when alternative lines already indent, as in your case, is beyond my competence in poetry [which ends with ... walls] Why your coding of poetry using spans should make the PG mechanizations so unhappy I don't see why. Be aware that Marcello's epubmaker [which is what PG uses to make epub and mobi] does considerable "rewriting" of the submitted html when converting to mobi (via epub) in order to try to work around the shortcomings of kindlegen -- where kindlegen doesn't handle many of the more "esoteric" [read: that which should be avoided] features of html, such as nesting and multiple inheritance (and float left, and float right, and ....) One common, and documented by Amazon, problem with kindlegen, is that the definition of mobi and the html to be submitted to kindlegen, does not include padding, nor does it include the merging of top and bottom margins. I think it also doesn't say that top and bottom margins are rounded to the nearest 1em. So, for example, if someone puts a top-margin: 0.5em bottom-margin: 0.em on their paragraph styles they are actually specifying that they want a 2em spacing between paragraphs in the mobi file. Ouch.