I noticed our source jars seemed really big for 1.5.0. At least one contributing factor is that, likely due to some change in the release script, the maven jars are being bundled in with the source code in our build directory. This runs afoul of the ASF policy on binaries in source releases - we should fix it in 1.5.1.
The issue (I think) is that we might invoke maven to compute the version between when we checkout Spark from github and when we package the source file. I think it could be fixed by simply clearing out the build/ directory after that statement runs.