It sounds like you have it reproduced, yes. Once you start using the editor you’ll notice how bad it is, like, you’d click on the viewport and all of a sudden your mouse is captured and you’re looking around until you click again. Then you click on a button, but it does nothing, so you have to click it again. That kind of thing.
Did you have to switch to 10.10 to reproduce it? So far I’ve not had a single problem with UE4 on Yosemite, it worked perfectly, at least until 4.4 arrived - now two major parts of the engine stopped working properly. Mouse input and skeletal animation.
I realise I’m somewhat on my own here, but wouldn’t it be best to avoid changes that are incompatible with 10.10 as that is releasing very soon. Keeping in mind that 4.3 worked perfectly.