The Vray Material updates very inconsistently in IPR. For example if I change the color from red to yellow it will not update at all. Only when I re-render does it appear correctly. Similarly, if I lower the glossiness or amount slightly the highlight completely disappears. Only when I re-render does it appear correctly again.
This appears to only happen with the Vray Material. The Maya materials seem to update fine in IPR when rendered with Vray. So do other Vray materials like the Fast SSS2. It only appears to be broken with the Vray Material.