It kind of all depends on what is considered sound practice. Back in the days of the classic gold standard, only central banks that were a bit off the beaten track held more interest bearing securities from other countries than they did gold or silver. Today, it's considered normal practice for central banks to hold interest bearing securities, and holding gold is considered OK for diversification, but you really don't want to hold too much, because it doesn't earn any interest.
So, in a world of floating currencies, it doesn't take much brainpower to figure out that if you buy enough of some other country's debt, you can run that country's currency up and yours down relative to each other, and goose your exports to that country. China, Japan, and even India all do this relative to the dollar. One would think that the 20 year stagnation of Japan would show that this policy is not some sort of economic Holy Grail, but I suppose the lesson is a hard one to learn.
This kind of currency war, because that's what it is, was foreseen by Paul Einzig all the way back in 1972 when he wrote "The Destiny of the Dollar" very shortly after Nixon took the dollar off the remaining fig leaf of a gold standard that was still around at that time.
So today we have all these crazy imbalances, and even after a big fat crisis, the situation still isn't being addressed. One wonders what it will take.