It is possible for (dried ground) ginger powder to give a bitter flavour, but I don't think that's what's happening here, or at least not alone.
If it's old and been badly stored (exposed to sunlight and /or not sealed properly), ground ginger loses its main flavour, but adding extra to make up for that does lead to a bitter and possibly unpleasant taste. I'm not sure whether whatever is responsible for that is always present, but normally masked, or if it's produced by the degradation of the compounds we want. I wouldn't expect the quantities you've used here to have that effect, though maybe if you used really heaped teaspoons it would, as well as being very gingery if the spice was fresh.
Other spices do this too, some more so. If your ginger is old, perhaps the other spices are too.