Surely, it cannot be the case that both argumentum ad ignorantiam and shifting the b.o.p. are both fallacies! Once again, the Logicians would have us believe we can't have our cake or eat it.
One of argumentum ad ignoramus and shifting the b.o.p. might, hypothetically speaking, be reasonably well-defined types of fallacy. But both? That's absurd!
Let's use Plasma's method to clear up the point. Consider this. Two would-be logicians, Gas and Liquid, are considering a point.
Gas asserts that B is true, without evidence.
Liquid now either goes along with this, or contests the claim. By contesting the claim, he must be asserting that B is false. This is because, as logicians like to point out (as in the principle of the excluded middle, or possibly that of bivalence), B is either true, or false, with no third possibility.
Gas now either "wins the argument", in Plasma's words, claiming no case to answer, or else finds himself on an equal footing with Liquid. One asserts "B is true", and the other asserts "B is false", or to put it more symmetrically, "(not B) is true".
Liquid now claims Gas is shifting the burden of proof, which is not cricket. The crowd (of logicians) goes wild.
Gas immediately cites argumentum ad ignorantiam: Liquid is merely claiming "not B" because (in ShadowNode's own words) "it is argued that something must be false because it hasn't been proved true". The logically-inclined spectators wait with bated breath...
Surely they can't both be right?! Or are we to believe the argument is tied?