I've had two bad ones with master grades. First was Master Grade Strike Freedom. I hated both the yellow gold plastic and the plated gold versions, so I bought the normal one and painted the parts. like an idiot i did this while all the parts were on the tree. when I assembled it all the parts were super tight. However, I didn't run into a problem until i assembled a hip joint, which basically tore apart. Long story short, the Strike Freedom got a fixed pose with that leg.
The second one was worse. After painting nd decaling the Sinanju (master grade) I top coated it while it was in its various parts. Putting it back together some of the joints had stiffened up. When I went to connect the last part, the top to the waist, it snapped. to have put all that work into it, only to break doing the last bit almost destroyed me. however, some plastic cement later and my master grade sinanju l;ooks fine... just doesnt do the twist.