Whenever I click on the adjustment brush tool in Develop mode, its circle of influence automatically expands to the maximum diameter.
Even when I try to contain the dimensions of the circle via the LR5's size slider or left bracket key, the adjustment brush diameter remains at the max diameter.
Hi - did you find the answer to this? We are having the same problem.
I would try restting the Prefernce file:
In Lightroom 6, you simply need to hold down Option-Shift (Alt-Shift on Windows) when you launch Lightroom, and it will prompt you to resetyour preferences. Click the Reset Preferences button to reset your user preferences, or click Start Normally to use the existing preference file