GI backflush's storage type seems not making sense

Dear all,

a little bit of background of myself and my R/3 setup for the following questions:

We are using WM-PP interface, which means we uses production supply and control circle in the setup.

I am not a PP person and am quite new in WM-PP area.

Questions:

3 - During material staging with standard SAP WM movement type 319, 3 component quantity are remove from storage type of 010 to interim supply storage type of 100 (i.e. as shown in the confirmed TO). Next, during backflush of goods issue (IM movement type: 261) when the production order is confirmed and is completed, the TO shown that the Source Storage type 010, and Destination interim type 914. I think this is wrong because since the material component is initial move from storage type of 010 (a storage type to keep the component stock) to interim storage type 100 during material staging, then how does

R/3 knock off the stock quantity in the interim 100 when during GI-backflush?