For cloth simulation items like buttons and buckles should be in the Rigid Decorated group not the Constrained group. They should also be part of the cloth item geometry, not separate props. I'm not familiar with MD but a solution may be to import the the jacket into Poser in a scene without a figure, import and position the buttons, try re-parenting them then. Then file>export wavefront obj from Poser with "weld bodyparts" selected. In a new scene with V4 loaded import the obj you just made, position and scale it. In the cloth room edit the rigid decorated group and select the buttons