Thanks for bringing this to the fore. At this instance, this appears to be an issue with the variable editor and not "repmat". You have mentioned that in the comment and it can also be illustrated by:
>> structElement = struct('a', '', 'b', '', 'c', );
>> RepSt = repmat(structElement, [4,1]);
I was able to reproduce this issue. I will add it to our records. On a side note, I would like to request you to not use "ans" as a variable. Using the reserved keywords as variable and function names should be avoided.