which brush exactly are you talking about?
if it's any of painter 11 and 12 real hard media brushes, look under window -> brush settings -> hard media and set up min. V min/H min values to 100 %;
if it's a bristle spray or pixel spray type of brushes, tilt is hard-coded into them
for anything else, look under brush settings -> size and angle and see if any of those are tilt-bound (but I can't think of any painter brush that is by default)
on the fourth day of glitchmas my painter™ gave to me
four random crashes, three broken brushes, two system hangups & one corrupted workspace