I would not use ML (or MLR) for indirect effects when the mediators are binary. You should use either WLSMV or Bayes estimation in which case you work with continuous latent response variables for the binary variables and this makes regular definitions of indirect effects reasonable. This is explained more fully in my paper on our website:
Muthén, B. (2011). Applications of causally defined direct and indirect effects in mediation analysis using SEM in Mplus.