I have a small but annoying problem with some of my layers in a map I am working on. I want to merge two layers. Layer one consists of a town and and layer two consists of the plow fields with blending options enabled. When I merge the two layers, the visual effects of the blending options on the second layer change. I haven't figured out why this was happening.

Sometimes I am able to work around this by merging the layer with blending options with an empty layer but that trick is not working this time around. Anyone know what I am doing wrong or what is going on here?

Using Photoshop 7. Layer 1 is a png image. Layer 2 is a hand drawn plow field drawn with pencil tool.