System Information
Windows 8.1, using CPU rendering

Blender Version
Broken: 2.76b and also the daily build from today.

Short description of error
Changing integrator presets does not trigger refreshing of the render preview

Exact steps for others to reproduce the error

0. Make sure you use the Cycles renderer.

1. Open any scene, it is helpful to have a glass shader in it, because they are very sensitive to the number of transmission bounces.
2. Set the viewport shading to "Rendered".
3. In the properties panel go to the Render Settings
4. Go to "Light Paths"
5. Set the integrator preset to "Direct Light"
6. Set some very low-quality settings, for example all light bounces to 0. The image is low-quality, the glass is black.
7. Change the preset to "Full Global Illumination"
8. Notice that the render preview does not change. If you set the viewport shading to "Solid", and then "Rendered" again, you can see the changes in the image, for example the glass is transparent again.