XM.SimpleModel is used by node, is mostly written in model_mixin.js, and does not use backbone-relational. The backbone-relational store creates a memory leak that we must not reckon with in node. XM.Model is used on our client side, is all of model_mixin.js plus an enormous amount of overrides in model.js. So you've just changed the behavior of XM.SimpleModel. It sounds like you're unaware of how these two different kinds of models are built, in which case I think it makes sense that you revert all of the attempts in this PR to "fix" the relationship between model_mixin.js and model.js.