In this paper, we document a paradigm gap in the combinatorial possibilities of verbs and aspect in Urdu: the perfective form of the -ya: kar construction (e.g. ro-ya: ki: cry-Pfv do.Pfv) is sharply ungrammatical in modern Urdu and Hindi, despite being freely attested in 19th century literature. We investigate this diachronic shift through historical text analysis, a large-scale corpus study which confirms the stark absence of perfective forms and subjective evaluation tasks with native speakers, who judge perfective examples as highly unnatural. We argue that this gap arose from a fundamental morphosyntactic conflict: the construction's requirement for a nominative subject and an invariant participle clashes with the core grammatical rule that transitive perfective assign ergative case. This conflict rendered the perfective form unstable, and its functional replacement by other constructions allowed the gap to become entrenched in the modern grammar.