After we patched drywall, we taped the seams and feathered drywall compound until it was smooth. We used kilz primer on the patched area. We then painted with an acrylic paint. After several weeks, we suddenly found a raised line in the paint, over the joint between the old drywall and the new piece of drywall. When we peeled the paint off, we expected to find a ridge in the mesh tape, but it is smooth. Can anyone help us figure out why the ridge developed in the paint? We don't want to repeat whatever mistake we made. Thanks.