FPS stuck at low frames after new scene viewed (vsync)

Without vsync I have 120+ fps but the occational tearing, with vsync I have the expected 60 fps.

However while using vsync the fps occationally gets stuck at 30 fps after viewing new scenes (looking at new directions, up a ladder or new chunks) and in order to get the fps back to 60 I need to go into options and toggle vsync on and off and it instantly goes back to 60 and stays there for quite some time until I yet again look at a new scene.

The reason I believe this to be a bug is because changing the vsync on and off fixes the problem instantly while waiting doesn't always fix the problem even after waiting 10 min, and when the fps does return it does so with a seemingly increased chance to go down to 30 fps again. (Similar effect to the old fixed bug in beta where chunks loaded extremely slow and you fixed it by reloading the all chunks)

Example: When I looked up from my mineshaft my fps dropped to 12 and stayed there, after I waiting about 30 sec for it to pass (without result) I opened the options and toggled vsync on and off which resulted in the fps instantly going back to 60. Whether or not the issue would automaticly be fixed if I looked away for a while or waited longer I cannot be sure, but I am almost certain this is not how it's meant to work.