I've never had to clear seal any Monokote edges in the decades that I have used it. Your iron is not hot enough. The iron should be hot to the point that the glue melts. When you do a seam of Monokote over Monokote, you can see the color come off on your shoe cover, which for me is a piece of white t-shirt. Of course then you want to run your iron over the seams just enough to get the top layer to melt to the bottom one, but not enough to drag the melted color over the finish. If you do that though, you can clean it up with Monokote solvent. When you are hot enough, these seams will not readily lift as you are describing happens to you. Good luck! Keep at it. Jon