Under the new EPA carb regs, all units have to have a vapor recovery, some will also have a charcoal canister (the old coffee can) Over filling could result in either raw fuel or the charcoal becoming contaminated with raw fuel which will damage the canister. Depending on where the vapor line is connected to the tank, I guess could result in getting fuel drawn into the carb through the low vacuum line, or damaging the charcoal canister, which would act like a clogged fuel cap ( be aware that the new systems do not have vented caps). The other thing is most small engine makers consider 1 ounces of oil usage per hour is considered normal.
Command engines are designed for about 2000 hours. Some will go longer some will go shorter. In defense of the engine and welder makers, this system is so new they haven't figured out all the bugs yet. Vapor recovery went into effect in 2011, and went into full effect this year. I am sure I will hear about this problem at my Kohler update in two weeks. If not I will mention it at the update school.