It seems random but I'm still experiencing having a material in my pack with a count of 0. The real issue is that if I have a stack of n raw or processed materials I often get back n-1 processed mats or items after processing or crafting and a remainder of 0 initial materials. I can move that 0 count item to the bank or around in my pack. A suggestion was to relog and the issue would resolve itself. I chose to simply discard the 0 count item to save relog time. In a discussion with Silvermoon it was suggested that this problem may only occur when processing or crafting from stacks of 10, 20, 30, etc counts. I was tired and didn't pay that close attention to what the original stack count was. I will in the future if it happens again on Wednesday. Another thing I had not thought to try was to leave the 0 count item in my pack and go out and harvest to see what would happen to the stack that started at 0. Sorry I can't provide a more detailed account. It was a long weekend, minus the hour for Daylight Saving Time, and I was tired. Still am. 
