Like other Arabic dialects, Cairene Egyptian Arabic (CEA) exhibits a two-pattern negation system: the circumfixal maa...š-pattern and the independent miš-pattern. However, when the negative polarity item (NPI) ʕumr (= "ever") occurs in pre-negative position in the sentence, the -š segment of the negation morpheme cannot be phonologically realized. Arguing that previous analyses of the structure of NegP in Arabic dialects fail to account for the puzzle of -š disappearance in CEA, I propose in this paper a solution to the puzzle in terms of a Split-Neg analysis of sentential negation in CEA, whereby the -š segment is treated as a separate head, subject to an interface condition that arguably regulates Spell-out of formal features in multiple licensing configurations in general. If correct, the analysis not only explains away a morphosyntactic puzzle from NPI contexts in CEA, but it also provides evidence that NPI phenomena, in addition to being a semantic dependency, may also involve formal feature licensing in a minimalist sense, with effects at the syntax-morphology interface.