It is not the handle tube that has rotated, but actually the cover. You cannot rotate the bar because the plugs on the end are square. I have had this handle for 3 years now and really like it because you can replace the grips--it is time for a new grip. The best route is to go down to M2. They have several different styles to choose from for $20.00. I replace mine every season.
When you do need to take the caps off, Remove the allen bolts completely and spray a little WD-40 down the hole. You need to pull the plugs straight out. I use a flat-head screwdriver between the plastic end-cap and the aluminum tube to get it started.