Paul, I think you're talking about the same thing you mentioned in the post I linked:
"BTW - there's an extra trick for you. If you scroll to the BOTTOM of the list of events in the Copy From list, you'll see that very last option will allow you to select to import actions from any other button in any other screen. We don't use it much because there is a lot of clean up you have to do to realign all the values, but sometimes it is useful."
I can't seem to find that option! I'm in the Edit Grid Column Action window for the object I want to copy an action set TO, and I've selected the "Copy Action" radio button, but the only options available are action sets from my current screen. I can't see any option about importing from another screen.
I've also just checked out the "Call Another Action Set" in Add Action List, and it also only seems to allow action sets made on the current page.
If it makes a difference, its not a button object I'm trying to copy actions to, but rather a link field I added to a grid. I'll go check and see if it only applies to button objects now.
Edit: Eureka! Apparently the 'copy actions from other screens' option is not available for grid link objects, but there is a workaround. If you add a button object to the screen and copy the action over to THAT button, then the action set becomes available as part of your same-screen action set options, and you can copy it into other objects, like my grid link object.
Interesting that the accessing of outside action sets is only available for buttons.. is that deliberate?