http://blog.ploeh.dk/2014/06/02/captive-dependency/
A (Transient) -> B (Singleton)
The problem with this small bit in the graph is if service B expects transient, but B itself is singleton - this means that for B only ever sees that first instance of A that the container gives it, and ignores the following instances thereafter.
This becomes a huge problem when A absolutely must be an instance per request e.g. UnitOfWork.