In looking at the cast list for the King and I, I noticed that Edward Baker-Duly is listed as understudying Murphy Guyer as Captain Orton, and Guyer is listed as Baker-Duly's understudy as Ramsey.
This choice seems strange to me, has it ever happened before?
"Grease," the fourth revival of the season, is the worst show in the history of theater and represents an unparalleled assault on Western civilization and its values. - Michael Reidel
I've had it happen in a regional production of How to Succeed where the producers decided to hire two different actors for Mr. Twimble and Wally Womper (roles that are often doubled in a lot of productions). Since the characters never appear onstage together they had the actors understudy each other.