FYI, this problem is still happening. I've taken to archiving the duplicate files so you may not immediately see it on my project, but the duplicates are definitely still being generated every time there's an alpha commit (perhaps other kinds, too) that follows a (intended, properly tagged through SVN client) release commit.
It looks like this is partially a duplicate report. They seem to be talking about the first part of the problem in this thread. Still, the bit about changelogs isn't mentioned there and hopefully the rest is still of some use to you.
I just made a commit to an addon repository and found that not only did it create a new file for the new commit, but a copy of the previous release seems to have been made. See here. There is the new commit, r172-alpha, and it is followed by two files called v0.99.1, the first of which has the same creation time as r172 (and the second of which is the actual previous release). The duplicate release seems to have propagated over to Curse, as well, since I manually edit change logs for release versions and I see the unedited version (which the duplicate uses since I didn't edit it) appears on Curse instead.
Also, if you click on r172-alpha, you'll see that the page says "No changelog provided." But I did provide changes when I made the commit, and even if I left that blank, it should still show recent parts of the commit log like previous alpha releases have done.