I was leveling my Northrend mining on a character and got it up to 39/80. I went back to the trainer and learned the Smelt Saronite recipe. This was confirmed in my General tab with the status text “You have learned how to create a new item: Smelt Saronite.” But when I open my mining profession book and look at Northrend mining I only see Smelt Cobalt as available. Smelt Saronite is still listed under Unlearned and has no Create All or Create buttons.
I determined that I had to clear my Filter selection (which defaulted it back to Cataclysm, the highest expansion mining that I’ve trained) and then select Northrend again for Smelt Saronite to properly show up as a usable smelting technique. Seems like the filter of known recipes is not being updated properly when you learn this until you force it to refresh.
Edit: Similar problem happened the next day when I learned Smelt Titanium and Titansteel.