I get Union{Some{Missing}, Some{Float64}} in both cases, using latest 1.4-rc and master. Not sure if you consider this fine or not, but they infer the same.
I am not quite sure why you need Some here though (unless some information was lost in condensing to an MWE).
I would suggest isolating the problem and just sending the method to the REPL without involving Revise (which I what I did to evaluate your code). I don’t see why inference should have anything to do with the latter, but if it does then that should be documented.