I fixed this yesterday! Turns out my printed circuit control board had some corrosion on the non visible side...so I had to remove the control board to see it. The corrosion was shorting a switch and after I cleaned it with rubbing alcohol, the heater now stays in "Pool mode" and doesn't...
which ever heater you buy, i'd try to get one that was manufactured in the same year or so...i just realized the one I bought was installed in 2011 but manufactured in 2008!
Power up the heater and it will eventually turn on to the spa setting! Even more concerning is it seems to register 260 degrees in the heater! Didn't realize until I woke up the next day and the heater was on when it shouldn't have been.
Here's a video of it in action...