I sent them an email and just received a response (they have great customer support):
"Upon seeing this inconvenience reported repeatedly in such a short amount of time, we proceeded to re test the iPad with the glass installed. We have come to the conclusion that this issue is with the device itself, not the glass. Across the board, manufacturers and consumers are having this similar issue with compatibility and usage of both items.
We did not find a root problem to the issue, yet when laying the device with the glass installed on a surface or holding with one hand and trying to utilize the device with the other, sensitivity and tactile function failed. Although one way that both seem to work properly is by slowing down along and adding pressure when touching, we know that it can become a hassle for a device as advanced as this one.
We know that not everyone is having this issue, and the ones that are having the issue do not seem to be having it the same as others. In which case makes it harder to point the main cause of such situation.
We did the same testing with the Skinomi TechSkin (sister product of the glass) and found no issues with tactile function, nor sensitivity. In which case do note that this would be a great option to go with in terms to protecting your device.
Skinomi offers a 100% Lifetime warranty on all of its products. We would be more than glad to send you a replacement of the TechSkin if you would be interested, under this warranty."