Problem with "Multiply"

I don't think I've seen this problem mentioned here before. Has anyone else come across it?

I'm using PS7.


I'm using this gradient (which is neither here nor there):



If I lessen the "multiply" setting, I'm getting the following results:

	Multiply 100%
	Multiply 60%
	Multiply 30%

What's with the lines? Is it something to do with the general graphics settings on my pc? Is it something else?

Any suggestions are greatly appreciated.