Take these two declarations:
spinner = ui.dSpinner(self, DataSource=some_obj, DataField="some_field")
print(spinner.DataSource, spinner.DataField)
and
spinner = ui.dSpinner(self)
spinner.DataSource = some_obj
spinner.DataField = "some_field"
print(spinner.DataSource, spinner.DataField)
They should be equivalent and print the same thing, but in the former case, the keyword arguments are lost, and the print() statement is empty. I've also seen it with other kw props like Top and Left, so it might be a general problem with dSpinner.