....And as such is probably something of an omission on Boeings part, as I'm pretty sure there are other types (does the 737? It's been a while!!) that WILL fly away from the MCP Alt in V/S.
Condition1:
The Aircraft is level at 5000 ft, MCP set at 5000ft.
Pilot selects VS and tries to get a descent,other pilot looks at him/her and starts laughing.
Condition2:
Aircraft is in descent in VS mode towards a lower MCP altitude,if the MCP is reset to an altitude setting higher than the aircraft actual altitude ,the VS will now be in an OPEN DeSCENt mode,therefore NO protection from the automatics.the other pilot will start yelling
Pilots proper procedures for MCP setting,calling FMa changes is the protection..(ie CDA,approaching MDA)
.
The VS needs a minimum of 100 ft mcp change to arm the mode.