Ratner's property and mild mixing for smooth flows on surfaces

Let $T=(T_t^f)_{t\in \mathbb{R}}$ be a special flow built over an IET $T : T \to T$ of bounded type, under a roof function f with symmetric logarithmic singularities at a subset of discontinuities of T. We show that $T$ satisfies so-called switchable Ratner's property. A consequence of this fact is that such flows are mildly mixing. Thus, on each compact, connected, orientable surface of genus greater than one there exist flows which are mildly mixing and not mixing.