  We provide evidence that a particular hidden supersymmetry, when combined
with half-maximal deformed global supersymmetry, implies that the theory is
invariant under duality rotations of the vector and spinor fields. Based on a
complete 8+8 supersymmetric model constructed recently, we argue that this
hidden supersymmetry happens if and only if there is a Born-Infeld dependence
on the Maxwell field strength and a Volkov-Akulov dependence on the Goldstino,
up to local non-linear field redefinitions. We have tested our proposal for the
N=2 superfield action with manifest N=2 supersymmetry and hidden N=2
supersymmetry at the level W^{10}, the highest level of deformation known for
this model. We have established that it is N=2 self-dual, although the
self-duality was not required in the original construction of this model.
Highlighting the utility of considering duality-conserving sources of
deformation, we can verify this invariance directly in an alternate
construction of this very same action.
