As "Radoslav Husar" mentioned there might be a explicit GC request from a deployed app (avoid with -XX:-DisableExplicitGC).
If not there is no exact point how a FullGC happen, it's a decision of the JVM depend on memory consumption of the different spaces and the frequence of minor GC.
Maybe jstat gives a hint (see oracle jstat documentation).
It might disapear with a new JVM version.
In other words I don't know exactly and if it do not disturb my application, e.g. happen very often, I don't care about ;)