Code files are overwritten, so methods being added is unlikely, UNLESS you have added include templates, but as you're using the demo, I don't expect you have added include templates because the SDK isn't a public download.
You can have duplicate methods / fields when you are using inheritance and you have a relation to the same entity in the supertype and in the subtype and in both entities you have a field mapped onto that relation with the same name.
Example, Employee <- Manager. Both have a relation to Department (works for in employee and manages in manager). If in both entities the name of the field mapped onto that relation is 'Department', the entity 'Manager' has the field twice, namely for its own relation and it also inherits the one from Employee.
Could you please check if this is the case?
There's currently not a check build in for this, this check is implemented in v2.5, currently in beta.