It looks like blown out highlights to me, I have had similar things happen. I'm not familiar with your scanner or the software you use but if there is a curve or histagram control in there you can remove the problem by adjusting the contrast. I suspect that you are trying to produce the visualised end result at the scanning stage, my advice is to forget it, remember, you can do a lot of work in PS after the scan.

Think of the scan being the same in digital terms as developing the negative in analogue terms. You would never knowingy overdevelop a film and blow out the highlights would you.

Can't resist this one Eric, if we had a digital forum this question would have been directed there?? Just my mischevious sense of humour as you well know.