Also - the smaller the diameter of the turntable the trickier it can be. I made some broad gauge turntables that were only 12 to 16 ft in diameter and they were unusuable until I realized the red and green arrows were not within that diameter. I ended up putting a 30 or 40 ft diameter part slightly below ground to make them work.
Let's be serious about this: I have the same problem. It happens only when some engines are over it. If you try when the turntable is empty, it works. But with some engines.. arrows are not where they have to be to turn. Is this a another bug..? I use 09, just in case anybody ask.