Well, from the you-know-what forum Yoshi said the alpha and beta version are "branched" into two lines 2 months ago, so what we will see in alpha version is not the newest build but only for stress test it meant to. While alpha test finished, all fixes will be merged into beta line and become new trunk.
(If you are familiar with software version control system such as "CVS" or "SVN" you will definite know what he means.)