trigger_and_read reads the instrument twice

[lucask07]

The bluesky stub plan trigger_and_read reads the instrument twice. See debug and ASCII strings below.

In [6]: x = trigger_and_read([osc.meas_phase])

In [7]: list(x)
trigger and read
skip rewind
inner trigger and read
Inner trigger
skip wait
reading in trigger and read
Ret = {}
Out[7]: :MEAS:PHAS? CHAN1, CHAN2
:MEAS:PHAS? CHAN1, CHAN2

[trigger: (ScpiSignalBase(read_name='osc_meas_phase', name='osc_meas_phase', parent='osc', value=0.0, timestamp=1532637723.0846121)), (), {'group': 'trigger-c087c1'},
 wait: (None), (), {'group': 'trigger-c087c1'},
 create: (None), (), {'name': 'primary'},
 read: (ScpiSignalBase(read_name='osc_meas_phase', name='osc_meas_phase', parent='osc', value=0.0, timestamp=1532637723.0846121)), (), {},
 save: (None), (), {}]

However, the sequence below only reads the instrument once. It seems that the trigger command is different.

In [4]: x = osc.meas_phase.trigger()
executing trigger
Signal trigger

In [5]: x = osc.meas_phase.read()
executing read
:MEAS:PHAS? CHAN1, CHAN2

In this sequence the trigger is actually from the SCPISignal. In the bluesky trigger_and_read its not clear where it comes from.