I've run into this issue before too. It stems from the fact *I think* that global objects maintain their layer Id (not layer name, the id) on layout transitions. Which totally makes sense.
Lets say in LayoutA that the layer with Id 2 has a name "midground". But in LayoutB the layer with Id 2 has a name of "foreground". So if your global object is on the layer with Id 2, going from LayoutA to LayoutB will make it seem like they changed layers from "midground" to "foreground". But C3 is simply keeping the layer id persistent of the global object.