You are probably pressing down on the middle mouse button too hard and are overriding the rotation reference you set.
After setting the rotation reference you should lightly press down on MB2 to rotate. If you press down too hard and a new target symbol appears at the mouse location, that becomes the new temporary rotation point.
can you make a movie of the steps you have done?
Alt+f5 to start recording
Alt+f7 to stop recording
like show in the movie it should work like it's shown