It is definitely intentional from my experience. You can backdate easily on journals but not so much on communities (probably to do with security but that's just what I assume). Personally when I ran into this problem, I deleted all the entries that were out of order and started adding the rest chronologically. Another thing you could do (that's a bit more mind-fucky) is to swap the html/dates for each entry around so that they appear in order. Definitely more of a hassle, but it should be easy to tell which order they should go in from the homepage (if not then you can look for the entry id before the '.html' in the url and sort them from lowest to highest). There may be a third or fourth option too, but these are just the two that I'm aware of. Either way I hope this helps!