I wrapped the bad fuse in a small cloth and used a pair of pliars to break the fuse open without putting any stress on the ends. One of the ends was not attached (the other end is very firmly attached and can't be pulled out by hand). The end of the filiment shows no sign of burning. In fact, it has a shiny coat of solder. So - cold solder joint.
Bottom line is you can't judge a fuse by its appearance
