Yes! I ran into that when I switched to track-ir too.
Good news and bad news:
Bad news: you will never get as good rear views with the TrackIR, compared to keyboard. I *think* this has to do with saving head positions, which you can do with TrackIR.
Good news: after you get the hang of it, you can get pretty close. Mine still takes some work to get good rear views, and it's not consistent. 3 things that REALLY helped me:
1) set up a profile in trackiR. Mine has a big deadzone, because I was getting seasick every time I moved my head just a little. Now it won't start panning unless I'm really meaning to.
2) map a button on your joystick or throttle to the Track-IR center (F12 by default). I use this A LOT. I have the reflector things, maybe that's why, I dunno, but my view can drift "off" every once in a while.
3) in AH settings, uncheck the track-ir setting for translation. Not sure the exact verbage used. I read somewhere to have that checked, and it made it really confusing for me. When I wanted to look back and to the side, I had to move my head in what seemed the opposite direction to me. After I switched it, it's much more straightforward. Not just sideways movement, but distance from your headrest.