Apache Derby is very often used opensource Java database. It is also known as Cloudscape or JavaDB. There are several branches available, but 10.3 is most used Derby branch today. It can be found in Websphere 7, Rational Software Team Concert/Foundation, Websphere CE 2.1 and probably in many many others. 10.1 and 10.2 branches are considered obsolete and 10.4 and 10.5 are considered too new and too risky for deployement.
First Derby release from branch usually contains lot of bugs which can include data corruption. Problem is that Derby team is making only 2 releases from each branch and not very often. Bugfixes are still backported to older branches (such as 10.3) but no releases are made. For example latest release from 10.3 branch is 10.3.3.0 (May 12, 2008 / SVN 652961) and there are 77 commits in 10.3 branch since that release with many bugfixes.
Put it simple: If you want to get latest bugfixes, which is very desirable especially if you plan to embed derby and ship it with your application which is not expected to be often updated, you need to compile Derby yourself.
Compiling Derby, especially older editions like 10.3, can be tricky. For information about building Derby see these two pages: Building Derby in wiki and BUILDING.txt in source tree. Because this information is not very accurate, some parts are too old or too new for 10.3, i will summarize building procedure:
Thats all. Finished Jars are in jars/insane subdirectory. Enjoy!