It looks like your master branch has the new on() method exposed in the service, but the Git tag for 2.3 that bower uses does not (so on() is not exposed). Looks like 2.3 tag is the same code as 2.2.
That's correct. 0.2.3 was just a documentation fix really. I've pushed out a new version(0.3.0) that includes some other fixes and the new on method. Let me know if you're having trouble finding it!
It looks like your master branch has the new on() method exposed in the service, but the Git tag for 2.3 that bower uses does not (so on() is not exposed). Looks like 2.3 tag is the same code as 2.2.