Java 8 and Jack weirdness with minifying

I have been using the latest and greatest for Android with Java 8 and Jack. This enables us to use the much awaited Lambdas in Android without having to resort to third party libraries like Retrolambda. The Jack compiler groups a few operations together, including minify which was previously done by Proguard. I have been encountering some weird issues with enabling minify for the release profile, running a simple clean assembleRelease consecutive times. Even a simple example with one button with the OnClickListener wired up with Butterknife tends to only work intermittently. Upon inspecting the created Dex, it seems like the dynamically generated classes from Butterknife were being stripped. Note that I DID NOT add anything to the Proguard configuration, so I expected them to be stripped out, but why were they not on every second or so compilation? So anyway, I have reluctantly reverted to Java 7 for now, but at least get the added bonus of quick compilation times and Instant Run actually working!