This, constant hot, to the dcomp/starter relay, is disconcerting to me...
I'm following your lead, Versy...

Also,.. considering an, on/off/on switch...  on/dcomp bypassed, off/no juice, on/hot to relay through dcomp... (could actually be wired to the stock ignition switch)...
off would be parked... dcomp bypassed would be normal running,.. and hot to relay through dcomp would be for TDC compression stoke, emergencies...
????...

Bad side... sounds more complicated than stock... (I hate complicated)
... better?... a good, simple, manual dcomp...

I await my highjacked, Versy brain solution...
Must be simple enough for a muppet...

Bot, if you will find that wire I told you about and make sure nothing is hitting it with power, then you can put a switch in it. It's not hot when you are riding,only when starting. Flip it on, hit start, turn it off. No starter engagement. That switch doesn't have to be a big current flow switch.

Just cut it leaving room to work, splice in a couple of wires and put a switch up under the frame. You flip it off and walk away with the key in it and nobody can fire up and ride away.
If im wrong, remove the switch and patch the wire. You're back to square one.
But I don't think I'm wrong. I made mine spin over by putting power to one of the wires.

You either have an intermittent short, putting power to that wire or the decompression timer is having an intermittent internal problem.
First place I would look is the always hot red wire running right next to the decompression timer.

A'righty then,.. dcomp bypassed and I'm still hearing random starter noise...

What I'm hearing is that 2 second wind down sound after you release the starter button... except it's happening while the engine is running...
...(a couple of times,.. I've heard it while backing the bike into a parking space, in gear with clutch pulled, other times goin' forward or idling in neutral)...
As a reminder,... I cleaned the starter button contacts, bypassed the dcomp...

Now,... on the way home... I disconnected the starter hot wire, and rode 25 miles home... no noise...

SOOOOO?... starter relay?... or could it be that fancy ratchity, starter torque limiter goin' funky?...
Versy?.. Dave?... I'm not too proud to be told what to think...

While the hot wire is off the starter you don't know if something is firing it. You could put a light on the wire up by the handlebars and if it comes on, you know something is trying to fire the starter.
You can put a switch in the hot wire to the solenoid, so it can't fire the starter.
Did you check out the red wire that runs by the decompression timer?

Stating the obvious..
You have an intermittent short that is either delivering 12 volts to the solenoid control winding OR the starter wire itself.

Disconnecting the wire at the starter didn't really eliminate any possibility.

Disconnect the starter wire AT the solenoid.  If the starter runs again, then you have a short from the starter wire to a hot wire.. somewhere.  Fortunately, it isn't a very long wire.

If not, then you have a short delivering 12 volts to the solenoid control winding..  Good luck finding that..