The distribution build uses the Ant copy task to copy jar files from the local maven repository (~/.m2/repository). It's possible that if the file copied in the first build had a newer timestamp than the newer version jar in the local maven repo, that ant would skip the copy. I'm not sure if this is the cause of what you saw, but it seems possible.
I'm not sure what is the best way to fix this. I could set the copy tasks to overwrite=true, to force a copy every time, but this might slow down incremental builds a little bit.
I'll collect more info the next time i try something on trunk, to ensure that its the timestamp problem.