Open Neutral indication on switched split wired receptacle circuit
 

In a residence I recently inspected, I used a circuit tester that can
test both GFCI and AFCI circuits. On several switched, split wired
receptacle circuits, the circuit tester indicates correct wiring with
the switch closed. When I open the switch to de-energize half of each
receptacle on the circuit, my tester indicates an open neutral.
Inspection of the wiring does not indicate a switched neutral. The
voltage measured on the switched circuit with the switch OPEN is 45-50
volts hot to neutral OR hot to ground. When I plug in a second tester
in a downstream receptacle, the voltage collapses to zero. Possible
causes we've considered are capacitive or inductive coupling and
defective switch that allows current leakage across the open switch.
The problem seems to be limited to one particular electrician and is
consistent on ALL switched split wired receptacle circuits. On AFCI
protected circuits, trip testing from the receptacles in bedrooms
results in correct operation of the breaker. When the circuit is
de-energized from the breaker panel, there is than NO indication of
open neutral and voltage on switched circuits goes to zero. Anyone
else experience that problem?