I would normally just shoot from the hip to go orbital from Kerbin, it's easy enough but this is EA and I wanted to yank the chains on this this to see how it has "improved"...ahem. To further delve down into this I just did an orbital ascent maneuver and used the nodes to plan it. When using the horizontal component to circularize, at just about the moment PE reaches LKO it decays and the AP goes nuts, as if I'm adding a radial component at the same time, hence my question in the opening of this thread. It is confusing because my AP is peaked at (enter LKO # here) and I'm applying a horizontal vector. The orbital planner seems to be including a vertical vector in as well because the orbit starts to behave that way. I don't have too many problems getting into orbit considering the circumstances of the game, but I'm trying to understand if this is a bugged instance of the maneuver node or an aspect of orbital mechanics that I do not understand yet.