From Krinkle's comment on T36733:
It [the function "postWithEditToken"] doesn't edit a page by default, it's used as a pre-processor basically to either continue or get an edit token first. You still need to set action=edit in the params (or something else). Looks like an mw.Api.prototype.edit function should be created separate from this that'll call it with action=edit. Not related to this bug [bug 34733] though, create a new enhancement bug for it and a patch if you like :)
Version: 1.19
Severity: enhancement