What exact setup do you have? Is the I-PAC connected and the computer on when you are trying this? Where are you plugging the keyboard into?
(I have a similar problem with a KeyWiz that I hot-swap into the PS/2 port. About 1/3 of the time, it will have an apparent stuck key when first plugged in. Pressing any other key or the same key once clears it, and I've never seen it re-occur until I unplugged it again, but it sounds like it might be similar).