Besides restarting the game and rebooting the turtle, have you also tried pickaxing the turtle and replacing it, or using the new
turtle.equipLeft /
turtle.equipRight commands on it? I'm guessing the addition of those latter two have something to do with it, as their introduction came with the possibility of removing the craft command from a given turtle.
I'd also be interested to know what happens if you copy the function pointer into a global variable, then check the contents of
that when the issue strikes.
(For those wondering what happens if you do that then remove the crafting table from a turtle, the function pointer remains, but does nothing when you call it.)