Thanks for your reply, but I see now that the the post ID in parentheses may be added by a different plugin, Admin Columns Pro (AC), which among other things provides its own ACF integration.
AC apparently intercepts the post list before the ACF Post Object select2 field processes the list of posts. Where the same ACF field appears by itself – outside of an admin column – the post IDs do not appear. I expect that that list will be modifiable via the ACF hook you specify. To modify the one that appears in the admin column setting, it looks like I’ll have to kludge something up. On the bright side, an AC “get_duplicates” function and its application look like useful models for dealing with ACF post-list output.
I still haven’t found exactly where or how the substitution occurs. If and when I do, I’ll post the information here, just so that ACF users can get something out of this thread, which otherwise I’d see about getting deleted.
