I catch myself time and time again reading a text backwards. Be it a short email, an article, or even a book. Most of the time I start from the end, read the last paragraph or page, and start jumping pages and paragraphs randomly backwards up to the start.
It may have been influenced by the fact that most magazines leave the best content to the end (so they can place a lot of ads in the middle).
Another explanation is the fact that less than 10% of everything I've ever read is fiction, where linear and progressive reading is the only way that makes sense.
Could it have any relation with the fact that I'm left-handed (I'd say 75% left-handed)? I looked around and couldn't find any scientific article or study about it.
Another theory I have is that it may be a habit that evolved from a known speed reading technique: doing a very fast skim on the text, basically trying to figure out how lengthy it is, how it is structured, what it talks about, where is the main point, how long is the conclusion and so on. So your eyes eventually get to the end of the text and then I get lazy to find where it actually started, so I just go on backwards from where I'm at.
Regardless of the reason behind it, I have found that it gives me better comprehension and helps me 'skim' the material objectively. Try it later and tell me how it went!