ok, provide the images, but using clamping 1 is from the "biased as fuck; anything can happen" domain :D
is any string option or tricks in config file to enable the bucket mode?
renderers.current.shading_renderEngine=0
with the latest release (2016.04.08) I have noticed a strange behavior of the VFB when switching from render/interactive render, the resize seems to be broken and the picture is offsetting to the bottom/right