After i stepped away from it for a bit and came back with a fresh spirit, i found the issue. Yesterday i kept staring at the calculations and wondering what the hell is going on and walked away from the computer in disgust.
Today i created a quick test with all the interface stripped away (not really, it's just hidden), put the intercpt angle and angle on bow at the intercept variables up on the left hand side readouts to monitor them, and then added a few lines of code to the Tactical Display to draw the intercept triangle. And there it is....
Apparently at some point in the performance improvement re-coding i forgot to add a call to update the intercept when the heading dial was turned.
So much easier when you can visualize it.
So yeah, im gonna fix that, and do some other improvements, and should have build 2 of the alpha back up in the next day or two.