FFS - Lean simulation - PULL mode

Hello everyone! 

I have a question about pull mode for FFS as simulation of lean manufacturing (pull signal from end of manufacturing cell to beginning).

• I have a simple manufacturing cell structure. (Page1 in attachment)
• All buffers, in / out zones, and workstation have „PULL“ mode
• In this setup, it is not working – flow stop on working cell (page 3)
• If I change workstation to push mode, then simulation is working fine (page 4). Workstation setup – page 5.

Why?