That's what I had initially. 

If you write spring.hornetq.mode=embedded, boot is unable to inject the value. If you don't have JSR-303 on the classpath you don't notice. If you do, you get an exception. 

Besides, that value is used in a SpEL expression to figure out which config to load so that's probably yet another issue we would have to deal with.

Don't get me wrong, I agree with you. This is also one of the reason I wanted a review on this.