We have the same issue. It would be useful to be able to Unmark for Action instead of having to "resolve" it.
Tracy Maurer suggested this as an improvement Structured Outcomes - Ability to unmark for Action on the Employee Engagement & Collaboration: Jive Platform
I see this issue, too. It's unfortunate how confusing it is.
I actually almost clicked Mark for Action the other day when looking for a way to remind myself to follow up on a thread. Even though I know that it's not a personal reminder, when I saw it in context, I almost forgot. There is no indicator that the whole group will see it. It would be great if Jive could do some user testing on this to try to eliminate the confusion.
An actual feature that will allow you to remind yourself (privately) to follow up on a thread or document would be great, too!