Some small bugs with Alpha-4 have surfaced and since not everybody likes to update to the nightly version (we all know that a work in progress is likely to break here and there for a while) There is now stable updates that just bring the most important fixes to your jME3 SDK install.
You just need to update when jMonkeyPlatform tells you theres available updates, the “stable” update center will be automatically added and the next time you update you will get all stable fixes installed to the SDK.
Cheers,
Normen