When painting into the prescale offset channel you must use the prescale offset tools. The tools on the palette are only for the offset channel, not the prescale offset channel (it's confusing, I know). Those tools are found on the Tools>>Paint Values>>Prescale Land Offset, Tools>>Paint Raise>>Prescale Land Offset, and Tools>>Paint Lower>>Prescale Land Offset menu items. I recommend just picking one of the tools and using the Operation dropdown on the toolbar to change between Value, Lower, and Raise.

On other thing is to make sure that you have the most recent version downloaded from the ProFantasy site (it should be 2.3.0.8 or later).

If the problem persists be sure to contact ProFantasy tech support and Linda should be able to help you.