This really isn't the issue that we are worried about. We are not worrying about HGH being dulled ... we are worried about your blood glucose levels soaring to uncomfortable heights.
The problem with carbs around an HGH injection is that for a matter of a few hours the HGH interferes with your body's ability to uptake glucose. That is a problem for many people over the course of a cycle. Intaking a lot of carbs at exactly the same time your body loses the ability to pull it out of your system elevates your blood glucose levels. We can theorize that the subsequent secretion of IGF will offset this in a few hours, but that is a pretty general observation and one that doesn't fit every user. Many folks (self included) can get some pretty impressive a1c readings while on HRT doses of HGH. That over time will result in some nasty sides that I would really rather not deal with.
The above is the reason we suggest no carbs around injection, not because we are afraid that we are somehow negating our exogenous HGH.