It's been a while, but if I remember correctly Play v1.x's 'magic' depended on Play v1 messing with Java bytecode. Well this in turn makes it harder to debug. This is no longer an issue with Play v2, but the magic (and the fun) are gone.
The reloading part of Play doesn't use bytecode manipulation, it simply creates a new classloader with the newly compiled stuff and then uses the new classloader on subsequent requests. There are other pieces of Play 1 & 2 that do bytecode manipulation. In Play 2 this is pretty minimal when using Java / EBean.
