Both the word “runaway” used in a general sense, and the term “runaway production” used to describe film work have been employed many ways. According to the Oxford English Dictionary, the first known use of the word “runaway” occurred in the sixteenth century. Initially, the term largely was used by property owners and referred to property running away. First there were runaway slaves, then horses. In the 18th and 19th centuries there were runaway elopements, railway trains, and wagons. Scribner’s in 1925 wrote of the “runaway market.”  However, only after World War II is runaway defined by workers to describe their jobs, and not defined by the property owners. “Runaway” was first used in union-related matters in 1949 to describe, “a plant transferred to destroy union effectiveness and to evade bargaining duties” (OED 1989:266). The transfer to motion-picture usage could have been suggested to some reader of a 1949 New York Times article about a film called Runaway, shooting on location in Yonkers, New York (Weiler, A. H. By Way of Report: Herman Shumlin and Vicotr Wolfson Mull Independent Picture–Of ‘Big Blonde’. The New York Times: x3, July 10, 1949).
In March 1950, the Hollywood trade paper Daily Variety discussed the “bartering away still more jobs of American film workers” in relationship to using European workers in Hollywood foreign film production. Without crediting a source, they called this phenomenon, “runaway” foreign production (Video, Divorcement Curbing Employment says SAG report, Daily Variety. Hollywood: 3, March 8, 1950.) If you know of an earlier reference, please let me know.
 Prior to the advent of runaway production as a film-labor related phenomenon during the 1930s, when the word “runaway” appeared in the newspapers in relationship to motion pictures, it had to do largely with young girls running away to Hollywood to become stars, or perhaps a runaway horse in relation to a motion picture shot.