After much investigation I have solved a problem that I was experiencing, but I wanted to give other users a heads up in case they encountered the same problem.
I am using AGS 126.96.36.199, and the SSH Description Module v1.06, using a location-following GUIMode configuration.
Here is what I was experiencing:
I slide the cursor up to the top of the screen, my custom Iconbar pops into view, and I click on a button. When I click on the bottom half of the button, there is never a problem. But when I click on the top half of a button, 80% of the time the button responds to my click, and the other 20% of the time, the button does not work; I must click on the bottom half of the button to get it to respond. When the top half of the button is not responding, the same is true for all the other buttons on the Iconbar, they too only respond to a bottom-half click.
The problem was solved by changing the Clickable property from True to False on the GUI used for the description.
I am guessing that although the Description Module was not displaying anything while over the Iconbar, an unseen GUI was still present, and sometimes interfered with the click.
In any case, thank you SSH for the module!