I can tell you that I've had that happen on dozens of occasions. Moreover, those watching the debate are usually swayed on the matter at hand more than the person you are arguing with.
And I never bring it up or say, "I told you so." I just note it, incorporate their new position with glee and move on.
The people I was referring to in my last comment I've been arguing these ideas for nearly two decades now and all that happens is either a 'I don't want to talk about this stuff' after they say stupid shit in my home or wait to pick the fight later with a new, more refined version of the old argument, which I skewer just as easily as before.
We're talking committed, Derrida/Foucault reading dyed-in-the-wool marxists here. They're not coming round until after the system crashes, if ever.
Yeah some people are intractable. They are locked into their paradigm and the only thing that causes a paradigm shift when someone is that LOCKED into how right they are is typically trauma, or some other shocking situation.