Operating system and graphics card
Broken: (example: 2.69.7 4b206af, see splash screen)
2.79(a), fresh from current Master
Short description of error
You can adjust the Proportional size in the Last operator. And the influence radius changes. But the proportional size radius in viewport still displays the old value, in both the header and the circle. And when you adjust the radius in the viewport, then the proportional size value in the Last operator snaps back to the value form the manipulation in the viewport instead of increasing from the value that you have typed in in the last operator Proportional Size edit box.
Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
Make a cube, enter edit mode. Enable Proportional Editing. Pull out a vertice. You will see the radius for proportional editing be displayed. And you can change it now by the scroll wheel for example.
The Proportional Size edit box updates the value.
Now change the value in the Edit box, and not by scroll wheel. The proportional influence changes. But the radius that displays the influence area stays still the same. And when you click at the transform widget, then the header shows the old value. We have now two different values for the same radius. Which i would classify as a bug.
Ideally the value in the viewport should update when you change the value in the edit box in the last operator panel.