Unicode error with Jenkins service (BB-4199)

I've tried to set up a service for my repository
radical / mean-machines to connect to my Jenkins installation via
both Jenkins and POST integration. I've failed dramatically, without any
debug or error information.

<<some of the private info removed>>

And got nothing. For both I see no hit from any outside world to my Apache proxy, and removing/adding the service brings no results as well. Last time I've checked I got some POST service response withing 10 seconds after doing //git push//, but no action at all on Jenkins.