Semi Finished will be debited by (3500 = 1500 + 1000 + 1000) only if it is maintained at Moving Average Price. SAP recommends SFG and FG to be maintained at Standard Price.
Please go into OMWB -> Simulation. Enter SFG, Plant and Movt Type as GR From Sub Contractor.
Check if the TE Keys and Account Assignment is correct. If possible post a screenshot.