An important customer has pointed out to me the hinging on his pieces isn't turning out well. The hinges look flat right after I do them, but the hinge and the paper it is attached to swells later leaving an unsightly "pillow". The paper isn't puckered- it's evenly swollen. I wish I had a photo, but I don't. What am I doing wrong? The hinges seem flat and dry as I'm doing them and I take care not to put too much paste on the hinge. The paste isn't watery. I cook it until it's almost a gel.