Like you, I question why one would release a beta without indication of what it fixes or adds. How can one test a beta if one doesn't know what to look for?
According to the Sticky (
http://forums.dlink.com/index.php?topic=10678.0) for the 1.13 Beta Code, these are the changes made. Note that a second build of the beta was released, which the moderator then graciously appended the change log entry for both builds.
DIR-825A1 release notes history.
====================================================
V 1.13NA, Build 02, 2010/01/21
1. Checksum: 0x042D8A7A
2. HNAP security hole
V 1.13NA, Build 01, 2009/12/22
1. Checksum: 0x042D9730
2. patch DNS relay
3. update: Advanced DNS descriptions