Yes, we cache these values for performance sake. typically you never need to access the value that you just sent.. ie in your example you are asking for the armMode but you just set the armMode 2 lines above.
If you really want to do this, or you need the non-cached current value, pass true as the second parameter:
def devarmMode = device.currentValue("armMode", true)
def devarmState = device.currentState("armMode", true)
The second parameter is "skip cache"
