I have allowed background saves, auto recovery etc, but disabling them doesn't do any good.
There was nothing else but these 4 lines in my test.ahk script. I also suspected that assigning data to the clipboard could cause the bookmark insertion, but as I wrote, I removed / added-back all the commands one-by-one until the above smallest misbehaving script remained. It is really perplexing: just reading the clipboard before ^c causes the side effects.
Obviously MS Word does something fancy with Ctrl-c. If I press Ctrl-c wait a second and press it again, nothing unusual happens. But if I press it twice in rapid fire, the Office Clipboard opens. Maybe, the problem is that Ctrl-c in WinWord copies the selection to the Windows clipboard *and* to the topmost position of the 24 Office clipboards. This procedure is smart: if you don't change the selection, just press Ctrl-c again no new Office clipboard position will be consumed. It shows, that MS Word remembers the last selection. The Office Help says:
The Office Clipboard is related to the system Clipboard in the following ways:
• When you copy multiple items to the Office Clipboard, the last item you copy is always copied to the system Clipboard.
• When you clear the Office Clipboard, the system Clipboard is also cleared.
• When you use the Paste command, the Paste button, or the shortcut keys (CTRL+V), you paste the contents of the system Clipboard, not the Office Clipboard.
It is not the speed. If I insert "Sleep 2000" before the "Send ^c" the bookmarks still appear.
Replacing ClipBoardAll with ClipBoard stops the bookmarking. I suspected that reading the clipboard involves a query, or list of objects and descriptors system call, and this has a side effect.
If you wish, you can make the script even shorter:
cb := ClipBoardAll
Mark something in Word, copy it to the clipboard by Ctrl-c. Do some editing, change to another window, save your work, etc, but upon returning to the original window, running the script by Alt-z bookmarks the last selection. You see that it is pretty sophisticated: the demon behind remembers the window and the position of the last selection, not only its content.