Phil,
I too use the brains that hood wrote fro spindle/feed override and at first they were a little "flaky" as you put it.
It turns out that I had to rename them in order for them to work properly. Go into your mach folder, double click the brains folder, locate the brain in question and
right click on it and select "rename". Choose a new name...(remember not to use any spaces in the new name) and try it again.
Worked for me....hope it does for you too.
Marc