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This worked for me: turn off whatever needed to be turned off in the Review tab (namely, expand the Tracking to get to the Track Changes Options, and set Reviewing Pane to "Off"), and then -- and that's the important bit -- SAVE the file and CLOSE it. Then reopen, and the problem is gone.
Without saving and closing it, the settings always reverted to that annoying behavior of the revisions pane appearing automatically. However, somehow saving and closing it actually made the changes to those settings take effect.