Ah yes, the phantom grid :) It's an old bug related to the way I render light in RPG Map (ie. a stupid & bad way).
I plan to revamp the lighting system in update 17 probably, as 16 is already on its way to release in the next few days. This should fix this phantom grid and increase performances in a huge way.
However, in the next update (ie. 16), I changed a few things with lighting render, and the phantom grid should be less obvious than here.