When we're trying to build protons near spawn at right corner usualy after 4 node(it's not 100% number,it's just number) it stop letting us build more protons...
BUT.When we start to build New proton node it let us build them at this spot.
So this thing just let us waste more du and mana for building\upgrading.
(now it doesn't realy needs them,but maybe in future xD)
Video: https://youtu.be/MEIK_FJ18-s