When you try to craft a quartz pillar block with quartz blocks in you inventory, a maximum of 2 can be craft at a time. This means that someone should place or toss one block to craft more. If you already have one in your inventory, only one will be crafted. In addition, the quartz blocks used in crafting are not two, but depend on how many quartz pillars are made (e.x., If you already have a pillar block in your inventory, and try to craft more, only one quartz block will be depleted).

Replicating this bug:
1) Have a stack of quartz in your inventory.
2) Craft them into quartz blocks.
3) Craft the blocks into quartz pillar blocks.

You will then see that one cannot have more than 2 in his inventory.