The common searchparameter 'patient' has two targets: Patient and Group.

The only base resourcetype for which Group is relevant is DeviceUseStatement.

For this resourcetype the fhirpath expression is DeviceUseStatement.subject. For all others it is either Xyz.patient or Xyz.subject.where(resolve() is Patient), thereby limiting it to Patient targets.

It would be easier and more consistent if the expression were changed to include DeviceUseStatement.subject.where(resolve() is Patient), and the target set to only 'Patient'.