A: When Howard Hughes is involved.
Montana Belle was a Republic Western starring Jane Russell as the title outlaw-ess. It was directed by Allan Dwan and shot in late 1948 (in Trucolor, which was owned by Republic’s Herbert J. Yates).
Jane Russell was under contract to Howard Hughes, who loaned her out to Republic. Once he saw Montana Belle, he bought the negative and shelved it till 1952, by which time things like The Paleface (1948) and His Kind Of Woman (1951) had made Russell a star — and Hughes figured a cheap little Western couldn’t damage her career too much.
Of course, by 1952 Hughes was the proud (though unfortunate) owner of RKO. So, Montana Belle became an RKO release — and Republic made a tidy profit on it without ever putting it in theaters.