The top texture of TNT has become not to randomly rotate. The file "assets\minecraft\blockstates\tnt.json" was changed in 15w49b, but the "change" wasn't included in the official change log. No one even mentioned this until now. Therefore, I think it can be called "a bug" instead of "a change".
Environment
Java 8u65, Windows 8
Intended as of MC-12959, the random rotation has been removed to fixthat issue