It's intended, though IMO it shouldn't be...can we please either remove obsoletion from nukes (A-Bombs) or move it back to a later tech? Those things take a long time to produce due to high cost and can't be bought, so that when one is beelining Advanced Ballistics (which is often a good idea for people who are interested in building up a nuclear arsenal) it happens frequently that one needs to delay researching that Tech just to be able to finish the first (!) nukes one has started building...plus there's no way that someone new to the game could know about this; in fact, I recently lost several turns of production in several Cities because I had forgotten about it again.