From a Merman biography by Bob Thomas on the 1950s Happy Hunting on Broadway : Once they were far along to sing on stage, Lamas noticed Merman sang all the love songs to the audience not him. He asked her about it.
Merman: I have been doing it that way since 193o. Lamas: Huh. That just proves you look your age!
Mary Martin who had the some status on Broadway as Merman just deferred to Merman the few times they worked together on TV or in concert. Mary was six years younger and it was not worth the effort.