Augmented my much edited posting above. From the OED1: "The related burglary is in legal A[nglo]F[rench] burlarie in Anglo-Latin burgaria, burgeria (early 13 c.), for which burglaria is found in the 16th c. The origin of the intrusive l in burglator, burglaria, and the corresponding Eng. forms is not clear; but the notion of Lambarde (1581) and later writers that the ending -lar represents AF ler-s, laroun (:- L. latro, latronem) thief, is contrary to the evidence." It seems to me from the French and Latin forms that the l came about from dissimilation (link).

Ceci n'est pas un seing.