JuMP will call setvartype! on the MPB model after loadproblem! if there are any non-continuous variables.
You should be aware that MPB will soon be replaced and unsuported in Julia 0.7 and JuMP 0.19 in favor of MathOptInterface (announcement). We’re getting closer to having basic MOI functionality working on the JuMP side and solver interfaces, but it’s not quite usable yet.