When implementing DDR3 SDRAM UniPHY and Altmemphy based memory controller, user will notice that during read operation, mem_dq bus does not give continuous burst even when there is no row address change. You will see this behavior in simulation as well.
You need to manually update CFG_RDBUFFER_ADDR_WIDTH in alt_mem_ddrx_controller.v HDL to fix it.
Set CFG_RDBUFFER_ADDR_WIDTH to:
Full rate - 8
Half rate - 7
Quarter rate - 6
This issue will be fixed in a future version of the Quartus® II software.