Vectorscope stops working when using curves

[#1]

When I try to adjust curves the vectorscope goes blank and only comes back if I click on the clip in the timeline. Any ideas of what is going on? 

[#2]

When I try to adjust curves the vectorscope goes blank and only comes back if I click on the clip in the timeline. Any ideas of what is going on? 

[#3]

I restarted Pr and it works now. Is this a common glitch?

[#4]

No, but rebooting sometimes does wonders.