It can happen that some time elapses between development on a release branch and those changes being merged back to the default branch, which is where the -nightly releases are created. The default branch is also the branch that you'll use when building from source unless you explicitly switch branches.
We just merged from the drcsim_2.5 branch back to default. So the next -nightly release will contain 2.5.x.
We merge fixes from the release branches back to default periodically. If you notice that something's missing from default, please let us know.