GIMP :: Unable To Set Up Parametric Brush

I am unable to set up parametric brushes that work correctly with a keyboard shortcut. At first when I assigned the keyboard shortcut to increase or decrease the parametric brush radius, as explained here Setting up GIMP for Artistic work, nothing happened when I pressed my new shortcut. Finally I, for reasons beyond me pressed the "reset size to brushes native size" button and it worked....sorta. It seems to work only within a limited range.

For instance. I reduce the radius all the way down to 1 then "magic size reset button" which sets size to 3, then I get a small brush. However when I increase size past 2 for the radius it doesn't increase further(the actual brush on the screen, the numbers change but that's it) until I press the size reset button. It's really frustrating because I can increase the radius using the keyboard from 2 to 9000 but I'm only getting a 2 pixel increase on the screen, unless I do the size reset then it jumps. I'm using Gimp 2.8.4 on windows 8 also set up to use a wacom tablet.