De-synonomize a taxon

[snacktavish]

https://tree.opentreeoflife.org/taxonomy/browse?id=483327
From Elliot: "Macronyx capensis and Motacilla capensis are very different taxa.
Similar common names and close in the tree, but definitely different"

They are both in this tree https://tree.opentreeoflife.org/curator/study/view/ot_2151
But if I try to add it as a taxon, I can't. The error shows "already appears in proposed taxa" but it's not in any amendments, I think that error because it already appears as a synonym.