Sorry, the problem is most probably related to SM-1738 (as you found out) and is still not resolved.
I find it depressing that this isn't resolved a year later. We're using Fuse/SMX 4.2 and none of the wsn2005 features work as advertised, none of the examples or documentation work for http - all calls break at this same point.
What is the point of having WSN2005 in your guides after all of this time? If you can't offer this over http to external pub/sub consumers why even use it? Internally?!?!? Why quote WSN as a feature when its been broken since 3.2.2 with no followups or attempts to fix it.
We actually needed WS Notification for our program. The hilarious thing is we were actually going to pay Fusesource for a support contract! HAHA. Yeah. ServiceMix is a quagmire - no upkeep, uninformative examples, hidden gotchas, and cryptic documentation that apparently is only meaningful for the handful of people developing the framework. I'll leave the hideous grammar and broken English alone this time. Its just sloppy.
We feel in part the same way. Their WSN implementation was what brought servicemix/fuse into the spotlight here.