So, you might have figured this out already, but I’ve been playing around with this more and found out that this happens when you move outside of the light’s attenuation radius whilst you’re facing away. The reason this spot light did not disable when you turned it slightly was because you turned the cone radius back onto the spot you were stood on. I think anyway.
So looks to me like the workaround, for now, is to increase the attenuation / cone radius of a light. This isn’t great of course, because doing that increases the likelihood of lights overlapping and eating up performance.