With the addition of the V_I/O pin in October of 1997, there is one stipulation in order for the P-CUT to stop motion when disconnected from GND: V_I/O must be pulled up.
If the V_I/O pin is not pulled up to either +5V or +24V, then motion may be produced regardless of whether the P-CUT is grounded or not (#2 and #3 below).
If the AUX-P pin is not pulled up (it is either grounded or not connected), then the V_I/O needs to be pulled up in order for the P-CUT to be able to stop motion. This time, the P-CUT must be connected to +5V to stop the motion. As long as the P-CUT is not pulled up (either it is grounded or not connected), then motion may occur (#4 and #5 below).
X = does not matter
open = no connection
GND = connected to Ground
+5V = connected to either 5 VDC or 24 VDC