Historically there was "e" as in the thirties the Soviets conducted reform spelling rules to bring the Ukrainian language to Russian rules. Previously, it was "center", "teater" and so on. Like in English. Now "e" is really pronounced, but not written. There were several attempts to change Soviet spelling, but they failed.
My information was heard on lectures on historical linguistics. However, now I managed to find only the text of spelling norms in edition of 1928, which specifies the use of the "-ер" in the words assimilated long ago - "маґістер, міністер, циліндер" etc. but "-p" in new loanwords. In particular - "театр, центр". http://r2u.org.ua/node/181 http://r2u.org.ua/node/245
So perhaps that my information is unreliable. In this case, I apologize.