Tab + 1/2 used to rotate textures, with both cancelling out of each other. It was also not "permanent", can't remember completely but either restarting the game or reloading the entity worked.
It doesn't this anymore, only a few blocks get rotated and those textures end up skewed. Can't rotate them back or reset it by restarting the game.
Only deleting the .jar file and re-downloading it seems to get it back to normal.
Don't care too much if this gets fixed or not, but putting some kind of option to enable to allow any Tab command to work seems recommended. Too many of them have the possibility to ruin your gameplay experience.