Good description indy727 - that's exactly what it is: a slight "let go". The car is still braking, just not as effectively as it was a moment before. It's never got me into bother, but on a few occasions it's taken me slightly closer to things than I wanted to be.
Just to expand on my earlier comment - I notice that the needle indicating power/regeneration pops up out of the blue regeneration sector and stays resolutely on 0 regardless of the current charging level of the battery.
Neil