Using the Automatic Precision setting (Brush Tip options), the Precision Level 4 lasts two intervals instead of one.

For example, setting Starting Brush Size to 0,00 px and Delta to 15,00 px, Precision Level 5 decreases to 4 at brush size 15,01 px (1 interval), but Precision Level 4 decreases to 3 only at brush size 45.01 px (2 intervals) instead of 30,01 px. The other levels decreases 1 interval correctly (3 to 2 at 60,01 px and 2 to 1 at 75,01 px).

I reproduced this using the Pixel, Color Smudge and Tangent Normal engines and other values for Starting Brush Size and Delta.

Reproducible: Always

Steps to Reproduce:
1. Check "Auto" next to the Precision slider at Brush Tip settings (Brush settings window);
2. The Precision Level won't refresh if you change the brush size with the Diameter slider, so close the brush settings window, change the brush size with the toolbar Size slider and open the brush settings window again.
3. Test different brush sizes to see when the Precision Level will change.

Actual Results:  
Precision Level 4 only decreases after 2 intervals.

Expected Results:  
Precision Level 4 should decrease after 1 interval.