Intermittent performance drops when moving head

I am currently experiencing some performance troubles with the Oculus Rift. I am using the native Unity implementation added in 5.1.0, and mostly it runs smoothly, but every now and then, there is a noticeable drop in performance for a single frame. It seems like VSync waits for an additional Frame, but I can't pinpoint a reason for this.
Profiling indicates that there are at least 11ms of the 13.333ms available at 75fps left for the CPU to idle, but sometimes the CPU waits ~23ms instead. Usually this coincides with a slight increase in rendering time (from ~1.5ms to ~2ms...in one single instance Rendering spiked to 12ms, but I wasn't able to reproduce this), but nothing to warrant this performance drop. (GPU Profiler shows Device.Present to double in time, while everything else stays the same)
Has anyone experienced a similar behaviour, or am I just mistaken in the assumption that OculusWaitForGPU is VSync?


Using Unity 5.1.1 with Oculus Runtime 0.6.0.0 (Direct Mode)