This happens with me for coal. I can see it on my active toolbar, but not in my inventory. It had fully disappeared on me (even allowing me to fill my inventory with other items) until I mined more, and had an empty slot in my tool bar, where it appeared (but still can't see it in my inventory). I can make blocks of coal from it, but cannot move it into another box. I'm afraid to remove it from my toolbar again, for fear I'll lose it!
Rowena
This happens with me for coal. I can see it on my active toolbar, but not in my inventory. It had fully disappeared on me (even allowing me to fill my inventory with other items) until I mined more, and had an empty slot in my tool bar, where it appeared (but still can't see it in my inventory). I can make blocks of coal from it, but cannot move it into another box. I'm afraid to remove it from my toolbar again, for fear I'll lose it!