It is also perfectly possible to press ALT HOLD for IAS/Mach window to open. Tried it on purpose yesterday, albeit on a -
500.
Punch the (unlit) ALT HOLD button, IAS/Mach window opens, FMA annouces framed MCP speed, ALT HLD remains.
I've also been taught to check modes on FMA (!), but also to understand MCP green lights - green light indicates a mode that can be disengaged, e.g. APP it is not. Under your scenario of intermediate level off, the FMA displays ALT HLD, but VNAV button light remains on. Thus if VNAV may be disnegaged, it must presumably be some sort of activated.
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Cheers,
FD.