|Taking a bow for the theatre at the theater.|
I found the following explanation (here), which seems to make a kind of ambiguous sense to me: "Garner’s and The AP Stylebook both list 'theater' as the preferred spelling. ... However ...'theater' has become the preference in American English only in the last 50 years or so, which makes some people reluctant to accept its spelling.
"Others have attempted to distinguish between theatre and theater, with theatre being an art form and theater being a building where theatre is performed. None of these, however, has caught on and none is borne out in actual usage.
"Unless 'theatre' is used in the proper name of a building, production company, etc., 'theater' is the correct spelling in American English."
So there you have it. Murky as ever.