+uvm_set_default_sequence=*,run_phase is causing two threads to spawn

I am running the UVM 1.2 examples code given in following link, which are there to demonstrate the UVM 1.2 new features.

http://www.edaplayground.com/s/4/1037

In the above code, the default sequence code can be controlled from command line with following code.

"+uvm_set_default_sequence=*,main_phase,seq_b"

If i use run_phase instead of main_phase, to control the default sequence, then same sequence will run twice instead of one.

"+uvm_set_default_sequence=*,run_phase,seq_b"

Two sequence threads are getting spawned parallelly, if i use run_phase to control default sequence.

I am expecting the behavior should be same whether i use run/main_phase. Not able to figure it out, why different behaviors are seen? 

This behavior is seen with UVM 1.2.