Need to investigate the BehaviorSubject as it likely has the same problem as Rx.Net as reported here: http://twistedoakstudios.com/blog/Post8424_deadlocks-in-practice-dont-hold-locks-while-notifying

Note that Subjects were just re-implemented but kept the same behavior and for the BehaviorSubject the race between returning the current value and subscribing for subsequent values appears to be wrong.

Use case:

onNext: 1 2 3 4 5 6 7 8 9
Observer: subscribe between 3 & 4 ... should receive 3 4 5 6 7 8 9

The likely bug is that in a race it could receive 3 6 7 8 9