The last preset you chose IS the last render-setting. So Reaper is doing, what you told it to do.
But I guess, this is confusing, if you've changed nothing after that and think, the preset isn't selected anymore.
You can have a look into the reaper-render.ini, which stores all the render-presets. Maybe you can find something helpful in there.
BTW: is this behavior already in place for some time or did it happen somewhere in the last updates?
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