Batch tracking updates

Batch tracking updates

I applaud the Zoho team for their recent updates to batch tracking information and even though I have 'chatted' to the Zoho team, I'm still batteling to understand the reasoning on the below.

We buy stock in bulk and it is received into the Bulk Warehouse.
      Bulk Warehouse = 23 900kg

We then pack some of this stock into a drum and it gets transferred to Drums Warehouse.
      Drums Warehouse = 900kg

Therefor the available stock in the bulk warehouse decreases
      Bulk Warehouse - 23 000kg

However, when looking at the Item Oveview screen/all warehouses, the quantity available is correct, but the Quantity In, increased by 900kg to 24 800kg.  This is the part that I don't understand. 
We ordered 23 900 and received 23 900, so why would the Quantity In keep increasing, everytime we move this same batch between warehouses?