Questions about Starter Circuit

I read the excellent articles on diagnosing problems in the starter circuit.  Really great information and easy to follow.  But I'm getting results from my 1974 CB200 that don't make sense based on the articles and would I love a little more detail to help me figure out what's happening.  Here's how I tested the starter button (as described in the article):

1. Disconnected the Yellow/Red (Y/R) wire going to the handle bars.
2. Connected my test probe to the positive terminal of the battery.
3. Touched the probe to the Y/R wire and then pressed the starter switch.

The results were different depending on the ignition/key switch:

• If the ignition switch is turned off or in the Accessory position, pressing the starter button lights up the probe.
• If the ignition switch is turned on, pressing the starter button does not light up the probe.

Doesn't that seem backward?  How could turning the key influence whether the switch connects properly?  Could this be caused by a short somewhere in the starter or headlight circuits?  Or is something cross wired, so it disables the switch when it's supposed to be enabled?  Is there any known/intended interaction between the starter switch and the ignition/key?

On a separate note, in the next section of the article it describes the solenoid trigger wires.  The black one brings the positive circuit up from the ignition switch, through the solenoid.  The Y/R wires come from the starter switch, where the connection to negative/ground gets made when you press the starter button. So, once again as described in the article:

1. I disconnected the Y/R wire off the solenoid.
2. Connected the test probe to the negative terminal of the battery.
3. Touched the test probe to the black and to the Y/R wires.

In both cases, when the ignition is turned on I get a completed circuit.  When the ignition is turned off, the probe doesn't light up.  That makes sense for the black wire (from negative terminal, through the probe, through the black wire, down to the ignition switch which can interrupt the circuit), and back to the positive terminal.  Right???

So in operation, the Y/R wire completes the part of the circuit that my test probe was making (from ground/negative to the solenoid).  Then the power goes through the solenoid and back down the black wire, as described above.  Is that right?  So when I put my test probe on the negative terminal and the Y/R trigger wire, I'm simulating the circuit that would normally be completed by the starter switch, right?

Thanks again for the great article!  Hopefully you can provide just a little more detail about expected results, so I can figure out what's supposed to be happening on my bike.